diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index feeee6d42..24a740924 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -7,7 +7,7 @@
 - Added a Julia eval backend (`language: "jl"`): a persistent subprocess Julia kernel that shares the standard agent tool bridge and evaluation model, supporting Julia REPL-style auto-display of results in a persistent session
 - Added configuration options `eval.rb` and `eval.jl` to enable or disable the Ruby and Julia backends, as well as `ruby.interpreter` and `julia.interpreter` paths for explicit runtime control
 - Added a Ruby eval backend (`language: "rb"`): a persistent subprocess Ruby kernel modeled on the Python kernel, speaking the same NDJSON protocol with isolated frame/stdout channels, clean SIGINT cancellation that preserves kernel state, and per-owner kernel cleanup. Ships the full prelude helper surface (`display`/`read`/`write`/`append`/`tree`/`diff`/`env`/`output`/`sort`/`uniq`/`counter`, the `tool.<name>` bridge proxy, and `completion`/`agent`/`parallel`/`pipeline`/`log`/`phase`/`budget`) over the shared loopback tool bridge, honors `local://` roots, and auto-displays the last expression IRB-style (suppressing assignments/definitions). Gated by the `eval.rb` setting and `PI_RB` env flag, with an optional `ruby.interpreter` override.
-- Added a Julia eval backend (`language: "jl"`): a persistent subprocess Julia kernel with the same NDJSON/result-display/tool-bridge model as the Python and Ruby eval runtimes, including `eval.jl` / `PI_JL` gating, `julia.interpreter` override support, persistent per-session state, clean cancellation, owner-based kernel cleanup, `local://` path roots, and the shared prelude helper surface for file I/O, tool calls, subagents, concurrency helpers, and budget access.
+- Added a Julia eval backend (`language: "jl"`): a persistent subprocess Julia kernel with the same NDJSON/result-display/tool-bridge model as the Python and Ruby eval runtimes, including `eval.jl` / `PI_JL` gating, `julia.interpreter` override support, persistent per-session state, clean cancellation, owner-based kernel cleanup, `local://` path roots, and the current Julia prelude helper surface (`display`/`read`/`write`/`append`/`tree`/`diff`/`env`/`output`, the `tool.<name>` bridge proxy, and bridge-backed `completion`/`agent`/`parallel`/`pipeline`/`log`/`phase`/`budget`, including structured `schema` parsing and `return_handle` DAG shaping).
 
 ### Changed
 
diff --git a/packages/coding-agent/src/config/settings-schema.ts b/packages/coding-agent/src/config/settings-schema.ts
index 628b6a1a1..8f8ce0772 100644
--- a/packages/coding-agent/src/config/settings-schema.ts
+++ b/packages/coding-agent/src/config/settings-schema.ts
@@ -122,7 +122,7 @@ export const TAB_GROUPS: Record<SettingTab, readonly string[]> = {
 	context: ["General", "Compaction", "Rules (TTSR)", "Experimental"],
 	memory: ["General", "Auto-Learn", "Mnemopi", "Hindsight"],
 	files: ["Editing", "Reading", "Read Summaries", "LSP"],
-	shell: ["Bash", "Eval & Python"],
+	shell: ["Bash", "Eval & Runtimes"],
 	tools: [
 		"Available Tools",
 		"Todos",
@@ -2969,7 +2969,7 @@ export const SETTINGS_SCHEMA = {
 		default: true,
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "Python Eval Backend",
 			description: "Allow the eval tool to dispatch Python cells to the IPython kernel",
 		},
@@ -2980,7 +2980,7 @@ export const SETTINGS_SCHEMA = {
 		default: true,
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "JavaScript Eval Backend",
 			description: "Allow the eval tool to dispatch JavaScript cells to the in-process runtime",
 		},
@@ -2991,7 +2991,7 @@ export const SETTINGS_SCHEMA = {
 		default: true,
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "Ruby Eval Backend",
 			description: "Allow the eval tool to dispatch Ruby cells to the persistent Ruby kernel",
 		},
@@ -3002,20 +3002,20 @@ export const SETTINGS_SCHEMA = {
 		default: true,
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "Julia Eval Backend",
 			description: "Allow the eval tool to dispatch Julia cells to the persistent Julia kernel",
 		},
 	},
 
-	// Python kernel knobs (consumed by the eval py backend and the /python slash command)
+	// Runtime knobs (consumed by eval backends and the /python slash command)
 	"python.kernelMode": {
 		type: "enum",
 		values: ["session", "per-call"] as const,
 		default: "session",
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "Python Kernel Mode",
 			description: "Keep the IPython kernel alive across eval calls or start fresh each time",
 		},
@@ -3025,7 +3025,7 @@ export const SETTINGS_SCHEMA = {
 		default: "",
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "Python Interpreter",
 			description:
 				"Optional path to an exact Python executable. When set, automatic Python runtime discovery is skipped.",
@@ -3036,7 +3036,7 @@ export const SETTINGS_SCHEMA = {
 		default: "",
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "Ruby Interpreter",
 			description:
 				"Optional path to an exact Ruby executable. When set, automatic Ruby runtime discovery is skipped.",
@@ -3047,7 +3047,7 @@ export const SETTINGS_SCHEMA = {
 		default: "",
 		ui: {
 			tab: "shell",
-			group: "Eval & Python",
+			group: "Eval & Runtimes",
 			label: "Julia Interpreter",
 			description:
 				"Optional path to an exact Julia executable. When set, automatic Julia runtime discovery is skipped.",
diff --git a/packages/coding-agent/src/eval/__tests__/julia-prelude.test.ts b/packages/coding-agent/src/eval/__tests__/julia-prelude.test.ts
new file mode 100644
index 000000000..fca3f0bfe
--- /dev/null
+++ b/packages/coding-agent/src/eval/__tests__/julia-prelude.test.ts
@@ -0,0 +1,77 @@
+import { afterEach, describe, expect, it } from "bun:test";
+import * as path from "node:path";
+import { $which, TempDir } from "@oh-my-pi/pi-utils";
+import { disposeJuliaKernelSessionsByOwner, executeJulia } from "../jl/executor";
+
+const HAS_JULIA = Boolean($which("julia"));
+const OWNER_ID = "julia-prelude-tests";
+
+describe.skipIf(!HAS_JULIA)("eval Julia prelude helpers", () => {
+	afterEach(async () => {
+		await disposeJuliaKernelSessionsByOwner(OWNER_ID);
+	});
+
+	it("supports tree keyword options and unified diff", async () => {
+		using tempDir = TempDir.createSync("@omp-eval-julia-helpers-");
+		await Bun.write(path.join(tempDir.path(), "a.txt"), "same\nold\n");
+		await Bun.write(path.join(tempDir.path(), "b.txt"), "same\nnew\n");
+		await Bun.write(path.join(tempDir.path(), "dir", "child.txt"), "child");
+
+		const result = await executeJulia(
+			`
+d = diff("a.txt", "b.txt")
+println("DIFF_DELETE=", occursin("-old", d))
+println("DIFF_ADD=", occursin("+new", d))
+t = tree(".", max_depth=2)
+println("TREE_CHILD=", occursin("child.txt", t))
+nothing
+`,
+			{
+				cwd: tempDir.path(),
+				sessionId: `julia-prelude-diff:${crypto.randomUUID()}`,
+				kernelOwnerId: OWNER_ID,
+				reset: true,
+			},
+		);
+
+		expect(result.exitCode).toBe(0);
+		expect(result.output).toContain("DIFF_DELETE=true");
+		expect(result.output).toContain("DIFF_ADD=true");
+		expect(result.output).toContain("TREE_CHILD=true");
+	});
+
+	it("supports output ranges, JSON queries, metadata, and ANSI stripping", async () => {
+		using tempDir = TempDir.createSync("@omp-eval-julia-output-");
+		const artifactsDir = path.join(tempDir.path(), "session-artifacts");
+		await Bun.write(path.join(artifactsDir, "alpha.md"), "one\ntwo\nthree\nfour");
+		await Bun.write(path.join(artifactsDir, "json.md"), JSON.stringify({ items: [{ name: "a" }, { name: "b" }] }));
+		await Bun.write(path.join(artifactsDir, "ansi.md"), "\u001b[31mred\u001b[0m");
+
+		const result = await executeJulia(
+			`
+println("RANGE=", replace(output("alpha", offset=2, limit=2), "\\n" => "|"))
+println("QUERY=", output("json", query=".items[1].name"))
+println("STRIPPED=", output("ansi", format="stripped"))
+meta = output("alpha", format="json")
+println("META=", meta["id"], ":", meta["char_count"] > 0)
+multi = output("alpha", "json")
+println("MULTI=", length(multi), ":", multi[1]["id"], ":", multi[2]["id"])
+nothing
+`,
+			{
+				cwd: tempDir.path(),
+				artifactsDir,
+				sessionId: `julia-prelude-output:${crypto.randomUUID()}`,
+				kernelOwnerId: OWNER_ID,
+				reset: true,
+			},
+		);
+
+		expect(result.exitCode).toBe(0);
+		expect(result.output).toContain("RANGE=two|three");
+		expect(result.output).toContain('QUERY="b"');
+		expect(result.output).toContain("STRIPPED=red");
+		expect(result.output).toContain("META=alpha:true");
+		expect(result.output).toContain("MULTI=2:alpha:json");
+	});
+});
diff --git a/packages/coding-agent/src/eval/jl/executor.ts b/packages/coding-agent/src/eval/jl/executor.ts
index db72a7e6e..dac5bb6e5 100644
--- a/packages/coding-agent/src/eval/jl/executor.ts
+++ b/packages/coding-agent/src/eval/jl/executor.ts
@@ -56,11 +56,20 @@ export interface JuliaResult {
 	stdinRequested: boolean;
 }
 
-interface JuliaSession {
+interface JuliaSessionOwners {
+	ownerIds: Set<string>;
+	hasFallbackOwner: boolean;
+}
+
+interface JuliaSession extends JuliaSessionOwners {
 	sessionKey: string;
 	sessionId: string;
+	cwd: string;
 	kernel: JuliaKernel;
-	owners: Set<string>;
+}
+
+interface StartingJuliaSession extends JuliaSessionOwners {
+	promise: Promise<JuliaSession>;
 }
 
 class JuliaExecutionCancelledError extends Error {
@@ -71,7 +80,7 @@ class JuliaExecutionCancelledError extends Error {
 }
 
 const sessions = new Map<string, JuliaSession>();
-const startingSessions = new Map<string, Promise<JuliaSession>>();
+const startingSessions = new Map<string, StartingJuliaSession>();
 const resettingSessions = new Map<string, Promise<void>>();
 
 function normalizeSessionCwd(cwd: string): string {
@@ -239,6 +248,7 @@ function buildKernelEnv(options: {
 }
 
 async function startKernel(cwd: string, options: JuliaExecutorOptions): Promise<JuliaKernel> {
+	requireRemainingTimeoutMs(options.deadlineMs);
 	const env: Record<string, string | undefined> = {};
 	const patch = buildKernelEnv(options);
 	if (patch) {
@@ -256,11 +266,18 @@ async function startKernel(cwd: string, options: JuliaExecutorOptions): Promise<
 	});
 }
 
-function attachOwner(session: JuliaSession, sessionId: string, ownerId: string | undefined): void {
-	if (ownerId) {
-		session.owners.add(ownerId);
-	} else {
-		session.owners.add(`unmanaged:${sessionId}`);
+function attachOwner(session: JuliaSessionOwners, sessionId: string, ownerId: string | undefined): void {
+	if (ownerId !== undefined) {
+		if (session.hasFallbackOwner) {
+			session.ownerIds.delete(sessionId);
+			session.hasFallbackOwner = false;
+		}
+		session.ownerIds.add(ownerId);
+		return;
+	}
+	if (session.hasFallbackOwner || session.ownerIds.size === 0) {
+		session.ownerIds.add(sessionId);
+		session.hasFallbackOwner = true;
 	}
 }
 
@@ -278,31 +295,39 @@ async function acquireSession(
 
 	const inFlight = startingSessions.get(sessionKey);
 	if (inFlight) {
-		const session = await waitForPromiseWithCancellation(inFlight, options);
-		attachOwner(session, sessionId, options.kernelOwnerId);
-		return session;
+		attachOwner(inFlight, sessionId, options.kernelOwnerId);
+		return await waitForPromiseWithCancellation(inFlight.promise, options);
 	}
 
+	let startingSession!: StartingJuliaSession;
 	const startPromise = (async () => {
-		try {
-			const kernel = await startKernel(cwd, options);
-			const session: JuliaSession = {
-				sessionKey,
-				sessionId,
-				kernel,
-				owners: new Set<string>(),
-			};
+		const kernel = await startKernel(cwd, options);
+		const session: JuliaSession = {
+			sessionKey,
+			sessionId,
+			cwd,
+			kernel,
+			ownerIds: new Set(startingSession.ownerIds),
+			hasFallbackOwner: startingSession.hasFallbackOwner,
+		};
+		if (startingSessions.get(sessionKey) === startingSession) {
 			sessions.set(sessionKey, session);
-			return session;
-		} finally {
-			startingSessions.delete(sessionKey);
 		}
+		return session;
 	})();
 
-	startingSessions.set(sessionKey, startPromise);
-	const session = await waitForPromiseWithCancellation(startPromise, options);
-	attachOwner(session, sessionId, options.kernelOwnerId);
-	return session;
+	startingSession = {
+		ownerIds: new Set(),
+		hasFallbackOwner: false,
+		promise: startPromise,
+	};
+	attachOwner(startingSession, sessionId, options.kernelOwnerId);
+	startingSessions.set(sessionKey, startingSession);
+	try {
+		return await waitForPromiseWithCancellation(startPromise, options);
+	} finally {
+		if (startingSessions.get(sessionKey) === startingSession) startingSessions.delete(sessionKey);
+	}
 }
 
 async function replaceSessionKernel(session: JuliaSession, cwd: string, options: JuliaExecutorOptions): Promise<void> {
@@ -310,38 +335,107 @@ async function replaceSessionKernel(session: JuliaSession, cwd: string, options:
 		sessionKey: session.sessionKey,
 	});
 	const oldKernel = session.kernel;
-	void oldKernel.shutdown({ timeoutMs: SHUTDOWN_GRACE_MS }).catch(() => {});
-
-	const kernelPromise = startKernel(cwd, options);
-	const kernel = await waitForPromiseWithCancellation(kernelPromise, options);
-	session.kernel = kernel;
+	const remaining = getRemainingTimeoutMs(options.deadlineMs);
+	await oldKernel
+		.shutdown(remaining !== undefined ? { timeoutMs: Math.max(0, remaining) } : undefined)
+		.catch(() => undefined);
+	if (sessions.get(session.sessionKey) !== session) {
+		throw new JuliaExecutionCancelledError(false);
+	}
+	requireRemainingTimeoutMs(options.deadlineMs);
+	const nextKernel = await startKernel(cwd, options);
+	if (sessions.get(session.sessionKey) !== session) {
+		await nextKernel.shutdown().catch(() => undefined);
+		throw new JuliaExecutionCancelledError(false);
+	}
+	session.kernel = nextKernel;
 }
 
 async function resetSession(sessionKey: string): Promise<void> {
-	const session = sessions.get(sessionKey);
+	const session = sessions.get(sessionKey) ?? (await startingSessions.get(sessionKey)?.promise.catch(() => undefined));
 	if (!session) return;
 	sessions.delete(sessionKey);
-	await session.kernel.shutdown({ timeoutMs: SHUTDOWN_GRACE_MS }).catch(() => {});
+	await session.kernel.shutdown({ timeoutMs: SHUTDOWN_GRACE_MS }).catch(() => undefined);
 }
 
 export async function disposeAllJuliaKernelSessions(): Promise<void> {
-	const active = Array.from(sessions.values());
-	sessions.clear();
+	const pending = [...startingSessions.values()].map(starting => starting.promise);
 	startingSessions.clear();
 	resettingSessions.clear();
-	await Promise.all(active.map(s => s.kernel.shutdown({ timeoutMs: SHUTDOWN_GRACE_MS }).catch(() => {})));
+	const started = await Promise.allSettled(pending);
+	const all = [...sessions.entries()];
+	for (const result of started) {
+		if (result.status !== "fulfilled") continue;
+		if (!all.some(([, session]) => session === result.value)) {
+			all.push([result.value.sessionKey, result.value]);
+		}
+	}
+	for (const [id, session] of all) {
+		if (sessions.get(id) === session) sessions.delete(id);
+	}
+	const results = await Promise.allSettled(all.map(([, session]) => session.kernel.shutdown()));
+	for (let i = 0; i < all.length; i += 1) {
+		const [id, session] = all[i];
+		const result = results[i];
+		if (result.status === "fulfilled" && result.value?.confirmed !== false) continue;
+		const reason = result.status === "rejected" ? result.reason : "not confirmed";
+		logger.warn("Julia kernel shutdown not confirmed", {
+			sessionId: session.sessionId,
+			sessionKey: id,
+			cwd: session.cwd,
+			reason,
+		});
+		if (!sessions.has(id)) sessions.set(id, session);
+	}
 }
 
 export async function disposeJuliaKernelSessionsByOwner(ownerId: string): Promise<void> {
-	const victims: JuliaSession[] = [];
-	for (const [key, session] of sessions) {
-		session.owners.delete(ownerId);
-		if (session.owners.size === 0) {
-			sessions.delete(key);
-			victims.push(session);
+	const toShutdown: JuliaSession[] = [];
+	const startingToShutdown: StartingJuliaSession[] = [];
+	for (const session of [...sessions.values()]) {
+		if (!session.ownerIds.has(ownerId)) continue;
+		if (session.ownerIds.size === 1) {
+			toShutdown.push(session);
+			continue;
 		}
+		session.ownerIds.delete(ownerId);
+	}
+	for (const [sessionKey, starting] of [...startingSessions.entries()]) {
+		if (sessions.has(sessionKey) || !starting.ownerIds.has(ownerId)) continue;
+		if (starting.ownerIds.size === 1) {
+			startingSessions.delete(sessionKey);
+			startingToShutdown.push(starting);
+			continue;
+		}
+		starting.ownerIds.delete(ownerId);
+	}
+	for (const session of toShutdown) {
+		if (sessions.get(session.sessionKey) === session) sessions.delete(session.sessionKey);
+	}
+	const started = await Promise.allSettled(startingToShutdown.map(starting => starting.promise));
+	for (const result of started) {
+		if (result.status !== "fulfilled") continue;
+		const session = result.value;
+		if (sessions.get(session.sessionKey) === session) sessions.delete(session.sessionKey);
+		toShutdown.push(session);
+	}
+	const results = await Promise.allSettled(toShutdown.map(session => session.kernel.shutdown()));
+	for (let i = 0; i < toShutdown.length; i += 1) {
+		const session = toShutdown[i];
+		const result = results[i];
+		if (result.status === "fulfilled" && result.value?.confirmed !== false) {
+			session.ownerIds.delete(ownerId);
+			continue;
+		}
+		const reason = result.status === "rejected" ? result.reason : "not confirmed";
+		logger.warn("Julia kernel shutdown not confirmed", {
+			sessionId: session.sessionId,
+			sessionKey: session.sessionKey,
+			cwd: session.cwd,
+			reason,
+		});
+		if (!sessions.has(session.sessionKey)) sessions.set(session.sessionKey, session);
 	}
-	await Promise.all(victims.map(s => s.kernel.shutdown({ timeoutMs: SHUTDOWN_GRACE_MS }).catch(() => {})));
 }
 
 async function executeWithKernel(
diff --git a/packages/coding-agent/src/eval/jl/prelude.jl b/packages/coding-agent/src/eval/jl/prelude.jl
index 698ba3b99..52ff323ef 100644
--- a/packages/coding-agent/src/eval/jl/prelude.jl
+++ b/packages/coding-agent/src/eval/jl/prelude.jl
@@ -76,6 +76,19 @@ function display_image(base64_str::String, mime_type::String = "image/png")
     return nothing
 end
 
+function __omp_emit_status(op::String, fields::AbstractDict=Dict{String, Any}())
+    status = Dict{String, Any}("op" => op)
+    for (k, v) in fields
+        status[string(k)] = v
+    end
+    Main.emit_frame(Dict(
+        "type" => "display",
+        "id" => Main.current_rid,
+        "bundle" => Dict("application/x-omp-status" => status)
+    ))
+    return nothing
+end
+
 # -------------------------------------------------------------------------
 # File helpers
 # -------------------------------------------------------------------------
@@ -154,8 +167,9 @@ function append(path, content)
     return resolved
 end
 
-function tree(path=".", max_depth=3, show_hidden=false)
+function tree(path=".", positional_max_depth=3, positional_show_hidden=false; max_depth=positional_max_depth, show_hidden=positional_show_hidden)
     base = string(path)
+    resolved = __omp_resolve_path(base)
     lines = String[]
     
     function walk(dir, prefix, depth)
@@ -183,7 +197,7 @@ function tree(path=".", max_depth=3, show_hidden=false)
         end
     end
     
-    walk(base, "", 1)
+    walk(resolved, "", 1)
     out = join(lines, '\n')
     
     Main.emit_frame(Dict(
@@ -192,7 +206,7 @@ function tree(path=".", max_depth=3, show_hidden=false)
         "bundle" => Dict(
             "application/x-omp-status" => Dict(
                 "op" => "tree",
-                "path" => base,
+                "path" => resolved,
                 "lines" => length(lines)
             )
         )
@@ -200,6 +214,366 @@ function tree(path=".", max_depth=3, show_hidden=false)
     return out
 end
 
+function __omp_lines_keepends(content::String)
+    parts = split(content, '\n'; keepempty=true)
+    if length(parts) == 1 && isempty(parts[1])
+        return String[]
+    end
+    lines = String[]
+    for i in eachindex(parts)
+        if i < length(parts)
+            push!(lines, string(parts[i], "\n"))
+        elseif !isempty(parts[i])
+            push!(lines, string(parts[i]))
+        end
+    end
+    return lines
+end
+
+function __omp_diff_ops(a::Vector{String}, b::Vector{String})
+    n = length(a)
+    m = length(b)
+    ops = Vector{Tuple{Symbol, Int, Int}}()
+    if n * m > 4_000_000
+        for i in 1:n
+            push!(ops, (:delete, i, 1))
+        end
+        for j in 1:m
+            push!(ops, (:insert, n + 1, j))
+        end
+        return ops
+    end
+
+    dp = [zeros(Int, m + 1) for _ in 1:(n + 1)]
+    for i in n:-1:1
+        for j in m:-1:1
+            dp[i][j] = a[i] == b[j] ? dp[i + 1][j + 1] + 1 : max(dp[i + 1][j], dp[i][j + 1])
+        end
+    end
+
+    i = 1
+    j = 1
+    while i <= n && j <= m
+        if a[i] == b[j]
+            push!(ops, (:equal, i, j))
+            i += 1
+            j += 1
+        elseif dp[i + 1][j] >= dp[i][j + 1]
+            push!(ops, (:delete, i, j))
+            i += 1
+        else
+            push!(ops, (:insert, i, j))
+            j += 1
+        end
+    end
+    while i <= n
+        push!(ops, (:delete, i, j))
+        i += 1
+    end
+    while j <= m
+        push!(ops, (:insert, i, j))
+        j += 1
+    end
+    return ops
+end
+
+function __omp_unified_diff(a::Vector{String}, b::Vector{String}, from_file::String, to_file::String, context::Int=3)
+    ops = __omp_diff_ops(a, b)
+    if !any(op -> op[1] != :equal, ops)
+        return ""
+    end
+
+    entries = [Dict{Symbol, Any}(:tag => tag, :ai => ai, :bi => bi, :text => tag == :insert ? b[bi] : a[ai]) for (tag, ai, bi) in ops]
+    changed = [i for i in eachindex(entries) if entries[i][:tag] != :equal]
+    groups = Vector{Tuple{Int, Int}}()
+    start = nothing
+    prev = nothing
+    for idx in changed
+        if start === nothing
+            start = idx
+            prev = idx
+        elseif idx - prev <= (2 * context) + 1
+            prev = idx
+        else
+            push!(groups, (start, prev))
+            start = idx
+            prev = idx
+        end
+    end
+    if start !== nothing
+        push!(groups, (start, prev))
+    end
+
+    out = IOBuffer()
+    write(out, "--- $from_file\n")
+    write(out, "+++ $to_file\n")
+    for (group_start, group_end) in groups
+        lo = max(group_start - context, 1)
+        hi = min(group_end + context, length(entries))
+        slice = entries[lo:hi]
+        a_start = nothing
+        a_count = 0
+        b_start = nothing
+        b_count = 0
+        for entry in slice
+            if entry[:tag] != :insert
+                if a_start === nothing
+                    a_start = entry[:ai]
+                end
+                a_count += 1
+            end
+            if entry[:tag] != :delete
+                if b_start === nothing
+                    b_start = entry[:bi]
+                end
+                b_count += 1
+            end
+        end
+        write(out, "@@ -$(a_start === nothing ? 1 : a_start),$a_count +$(b_start === nothing ? 1 : b_start),$b_count @@\n")
+        for entry in slice
+            prefix = entry[:tag] == :equal ? " " : (entry[:tag] == :delete ? "-" : "+")
+            text = string(entry[:text])
+            if !endswith(text, "\n")
+                text *= "\n"
+            end
+            write(out, prefix * text)
+        end
+    end
+    return String(take!(out))
+end
+
+function Base.diff(a::AbstractString, b::AbstractString)
+    path_a = __omp_resolve_path(string(a))
+    path_b = __omp_resolve_path(string(b))
+    lines_a = __omp_lines_keepends(open(path_a, "r") do io
+        Base.read(io, String)
+    end)
+    lines_b = __omp_lines_keepends(open(path_b, "r") do io
+        Base.read(io, String)
+    end)
+    out = __omp_unified_diff(lines_a, lines_b, path_a, path_b)
+    __omp_emit_status("diff", Dict{String, Any}(
+        "file_a" => path_a,
+        "file_b" => path_b,
+        "identical" => isempty(out),
+        "preview" => first(out, min(500, length(out)))
+    ))
+    return out
+end
+
+function __omp_apply_query(data, query)
+    if query === nothing || isempty(string(query))
+        return data
+    end
+    q = strip(string(query))
+    if startswith(q, ".")
+        q = length(q) == 1 ? "" : q[2:end]
+    end
+    if isempty(q)
+        return data
+    end
+
+    tokens = Vector{Tuple{Symbol, Any}}()
+    buf = ""
+    chars = collect(q)
+    i = 1
+    while i <= length(chars)
+        ch = chars[i]
+        if ch == '.'
+            if !isempty(buf)
+                push!(tokens, (:key, buf))
+                buf = ""
+            end
+        elseif ch == '['
+            if !isempty(buf)
+                push!(tokens, (:key, buf))
+                buf = ""
+            end
+            j = i + 1
+            while j <= length(chars) && chars[j] != ']'
+                j += 1
+            end
+            inner = j > i + 1 ? String(chars[(i + 1):(j - 1)]) : ""
+            if startswith(inner, "\"") && endswith(inner, "\"")
+                push!(tokens, (:key, length(inner) <= 2 ? "" : inner[2:end-1]))
+            else
+                push!(tokens, (:index, parse(Int, inner)))
+            end
+            i = j
+        else
+            buf *= string(ch)
+        end
+        i += 1
+    end
+    if !isempty(buf)
+        push!(tokens, (:key, buf))
+    end
+
+    current = data
+    for (kind, value) in tokens
+        if kind == :index
+            if !(current isa AbstractVector)
+                return nothing
+            end
+            idx = Int(value)
+            julia_idx = idx >= 0 ? idx + 1 : length(current) + idx + 1
+            if julia_idx < 1 || julia_idx > length(current)
+                return nothing
+            end
+            current = current[julia_idx]
+        else
+            key = string(value)
+            if !(current isa AbstractDict) || !haskey(current, key)
+                return nothing
+            end
+            current = current[key]
+        end
+    end
+    return current
+end
+
+function __omp_json_text(value)
+    if value === nothing
+        return "null"
+    end
+    try
+        return Main.json_serialize(value)
+    catch
+        return string(value)
+    end
+end
+
+function __omp_optional_int(value, default::Int)
+    if value === nothing
+        return default
+    elseif value isa Integer
+        return Int(value)
+    elseif value isa AbstractFloat
+        return Int(trunc(value))
+    elseif value isa AbstractString
+        return parse(Int, value)
+    end
+    return Int(value)
+end
+
+function output(ids...; format="raw", query=nothing, offset=nothing, limit=nothing)
+    artifacts_dir = get(ENV, "PI_ARTIFACTS_DIR", "")
+    if isempty(artifacts_dir)
+        session_file = get(ENV, "PI_SESSION_FILE", "")
+        if isempty(session_file)
+            __omp_emit_status("output", Dict{String, Any}("error" => "No session file available"))
+            error("No session - output artifacts unavailable")
+        end
+        artifacts_dir = replace(session_file, r"\.[^.]*$" => "")
+    end
+    if !isdir(artifacts_dir)
+        __omp_emit_status("output", Dict{String, Any}("error" => "Artifacts directory not found", "path" => artifacts_dir))
+        error("No artifacts directory found: $artifacts_dir")
+    end
+    if isempty(ids)
+        __omp_emit_status("output", Dict{String, Any}("error" => "No IDs provided"))
+        error("At least one output ID is required")
+    end
+    if query !== nothing && (offset !== nothing || limit !== nothing)
+        __omp_emit_status("output", Dict{String, Any}("error" => "query cannot be combined with offset/limit"))
+        error("query cannot be combined with offset/limit")
+    end
+
+    results = Vector{Dict{String, Any}}()
+    not_found = String[]
+    for output_id_value in ids
+        output_id = string(output_id_value)
+        output_path = joinpath(artifacts_dir, output_id * ".md")
+        if !isfile(output_path)
+            push!(not_found, output_id)
+            continue
+        end
+
+        raw = open(output_path, "r") do io
+            Base.read(io, String)
+        end
+        raw_lines = split(raw, '\n'; keepempty=true)
+        total_lines = length(raw_lines)
+        selected = raw
+        range_info = nothing
+
+        if query !== nothing
+            json_value = try
+                Main.json_parse(raw)
+            catch err
+                __omp_emit_status("output", Dict{String, Any}("id" => output_id, "error" => "Not valid JSON: $(err)"))
+                error("Output $output_id is not valid JSON: $(err)")
+            end
+            result_value = __omp_apply_query(json_value, query)
+            selected = __omp_json_text(result_value)
+        elseif offset !== nothing || limit !== nothing
+            start_line = max(1, __omp_optional_int(offset, 1))
+            if start_line > total_lines
+                __omp_emit_status("output", Dict{String, Any}("id" => output_id, "error" => "Offset $start_line beyond end ($total_lines lines)"))
+                error("Offset $start_line is beyond end of output ($total_lines lines) for $output_id")
+            end
+            effective_limit = limit === nothing ? total_lines - start_line + 1 : __omp_optional_int(limit, total_lines - start_line + 1)
+            end_line = min(total_lines, start_line + effective_limit - 1)
+            selected = join(raw_lines[start_line:end_line], '\n')
+            range_info = Dict{String, Any}("start_line" => start_line, "end_line" => end_line, "total_lines" => total_lines)
+        end
+
+        if format == "stripped"
+            selected = replace(selected, r"\x1b\[[0-9;]*m" => "")
+        end
+
+        if format == "json"
+            entry = Dict{String, Any}(
+                "id" => output_id,
+                "path" => output_path,
+                "line_count" => query !== nothing ? length(split(selected, '\n')) : total_lines,
+                "char_count" => query !== nothing ? length(selected) : length(raw),
+                "content" => selected
+            )
+            if range_info !== nothing
+                entry["range"] = range_info
+            end
+            if query !== nothing
+                entry["query"] = query
+            end
+            push!(results, entry)
+        else
+            push!(results, Dict{String, Any}("id" => output_id, "content" => selected))
+        end
+    end
+
+    if !isempty(not_found)
+        available = sort([replace(name, r"\.md$" => "") for name in readdir(artifacts_dir) if endswith(name, ".md")])
+        msg = "Output not found: $(join(not_found, ", "))"
+        if !isempty(available)
+            shown = available[1:min(20, length(available))]
+            msg *= "\n\nAvailable outputs: $(join(shown, ", "))"
+            if length(available) > 20
+                msg *= " (and $(length(available) - 20) more)"
+            end
+        end
+        __omp_emit_status("output", Dict{String, Any}("not_found" => not_found, "available_count" => length(available)))
+        error(msg)
+    end
+
+    if length(ids) == 1
+        if format == "json"
+            __omp_emit_status("output", Dict{String, Any}("id" => string(ids[1]), "chars" => results[1]["char_count"]))
+            return results[1]
+        end
+        __omp_emit_status("output", Dict{String, Any}("id" => string(ids[1]), "chars" => length(results[1]["content"])))
+        return results[1]["content"]
+    end
+
+    if format == "json"
+        __omp_emit_status("output", Dict{String, Any}("count" => length(results), "total_chars" => sum(r["char_count"] for r in results)))
+        return results
+    end
+
+    __omp_emit_status("output", Dict{String, Any}("count" => length(results), "total_chars" => sum(length(r["content"]) for r in results)))
+    return results
+end
+
 function env(key=nothing, value=nothing)
     if key === nothing
         items = Dict{String, String}()
@@ -344,20 +718,68 @@ const tool = OmpToolProxy()
 # Agent calls
 # -------------------------------------------------------------------------
 
-function completion(prompt::String; kwargs...)
-    args_dict = Dict{String, Any}("prompt" => prompt)
+function completion(prompt::String; model="default", system=nothing, schema=nothing, kwargs...)
+    args_dict = Dict{String, Any}("prompt" => prompt, "model" => model)
+    if system !== nothing
+        args_dict["system"] = system
+    end
+    if schema !== nothing
+        args_dict["schema"] = schema
+    end
     for (k, v) in kwargs
         args_dict[string(k)] = v
     end
-    return __omp_call_bridge("completion", args_dict)
+    res = __omp_call_bridge("__completion__", args_dict)
+    text = res isa AbstractDict ? get(res, "text", res) : res
+    return schema === nothing ? text : Main.json_parse(string(text))
 end
 
-function agent(prompt::String; kwargs...)
+function agent(prompt::String; agent_type="task", model=nothing, label=nothing, schema=nothing, return_handle=false, kwargs...)
     args_dict = Dict{String, Any}("prompt" => prompt)
-    for (k, v) in kwargs
-        args_dict[string(k)] = v
+    if agent_type !== nothing
+        args_dict["agentType"] = agent_type
     end
-    return __omp_call_bridge("agent", args_dict)
+    if model !== nothing
+        args_dict["model"] = model
+    end
+    if label !== nothing
+        args_dict["label"] = label
+    end
+    if schema !== nothing
+        args_dict["schema"] = schema
+    end
+    handle_result = return_handle
+    for (k, v) in kwargs
+        key = string(k)
+        if key == "agent_type" || key == "agentType"
+            args_dict["agentType"] = v
+        elseif key == "return_handle" || key == "returnHandle"
+            handle_result = Bool(v)
+        else
+            args_dict[key] = v
+        end
+    end
+    res = __omp_call_bridge("__agent__", args_dict)
+    text = res isa AbstractDict ? get(res, "text", res) : res
+    parsed = schema === nothing ? text : Main.json_parse(string(text))
+    if !handle_result
+        return parsed
+    end
+    details = res isa AbstractDict ? get(res, "details", nothing) : nothing
+    if !(details isa AbstractDict) || get(details, "id", nothing) === nothing
+        return Dict{String, Any}("text" => text, "output" => text, "handle" => nothing, "id" => nothing, "agent" => nothing)
+    end
+    node = Dict{String, Any}(
+        "text" => text,
+        "output" => text,
+        "handle" => "agent://" * string(get(details, "id", nothing)),
+        "id" => get(details, "id", nothing),
+        "agent" => get(details, "agent", nothing)
+    )
+    if schema !== nothing
+        node["data"] = parsed
+    end
+    return node
 end
 
 function Base.log(message::AbstractString)
@@ -394,8 +816,9 @@ end
 
 function _concurrency_limit()
     try
-        limit_val = __omp_call_bridge("concurrency-bridge", Dict{String, Any}())
-        return limit_val isa Number ? Int(limit_val) : 0
+        snap = __omp_call_bridge("__concurrency__", Dict{String, Any}())
+        limit_val = snap isa AbstractDict ? get(snap, "limit", 0) : snap
+        return limit_val isa Number ? max(Int(limit_val), 0) : 0
     catch
         return 0
     end
@@ -456,34 +879,52 @@ end
 # Budget
 # -------------------------------------------------------------------------
 
-struct OmpBudgetHardProxy end
+struct OmpBudgetProxy end
 
-function Base.getproperty(::OmpBudgetHardProxy, sym::Symbol)
-    if sym === :total
-        return __omp_call_bridge("budget:total", Dict{String, Any}())
-    elseif sym === :spent
-        return () -> __omp_call_bridge("budget:spent", Dict{String, Any}())
-    elseif sym === :remaining
-        return () -> __omp_call_bridge("budget:remaining", Dict{String, Any}())
+function __omp_budget_snapshot()
+    try
+        snap = __omp_call_bridge("__budget__", Dict{String, Any}())
+        return snap isa AbstractDict ? snap : Dict{String, Any}()
+    catch
+        return Dict{String, Any}()
     end
-    error("Unknown budget hard metric: $sym")
 end
 
-struct OmpBudgetProxy
-    hard::OmpBudgetHardProxy
+function __omp_budget_int(value, default::Int=0)
+    if value isa Integer
+        return Int(value)
+    elseif value isa AbstractFloat
+        return Int(trunc(value))
+    elseif value isa AbstractString
+        try
+            return parse(Int, value)
+        catch
+            return default
+        end
+    end
+    return default
 end
 
-function Base.getproperty(bp::OmpBudgetProxy, sym::Symbol)
-    if sym === :hard
-        return bp.hard
-    elseif sym === :total
-        return __omp_call_bridge("budget:total", Dict{String, Any}())
+function Base.getproperty(::OmpBudgetProxy, sym::Symbol)
+    if sym === :total
+        snap = __omp_budget_snapshot()
+        return get(snap, "total", nothing)
+    elseif sym === :hard
+        snap = __omp_budget_snapshot()
+        return get(snap, "hard", false) == true
     elseif sym === :spent
-        return () -> __omp_call_bridge("budget:spent", Dict{String, Any}())
+        return () -> __omp_budget_int(get(__omp_budget_snapshot(), "spent", 0), 0)
     elseif sym === :remaining
-        return () -> __omp_call_bridge("budget:remaining", Dict{String, Any}())
+        return () -> begin
+            snap = __omp_budget_snapshot()
+            total = get(snap, "total", nothing)
+            if total === nothing
+                return Inf
+            end
+            return max(0, __omp_budget_int(total, 0) - __omp_budget_int(get(snap, "spent", 0), 0))
+        end
     end
     error("Unknown budget metric: $sym")
 end
 
-const budget = OmpBudgetProxy(OmpBudgetHardProxy())
+const budget = OmpBudgetProxy()
diff --git a/packages/coding-agent/src/eval/jl/runner.jl b/packages/coding-agent/src/eval/jl/runner.jl
index d63c4949d..62c466e51 100644
--- a/packages/coding-agent/src/eval/jl/runner.jl
+++ b/packages/coding-agent/src/eval/jl/runner.jl
@@ -14,6 +14,16 @@ redirect_stdin(devnull)
 
 global current_rid = nothing
 const write_lock = ReentrantLock()
+const drain_state_lock = ReentrantLock()
+
+mutable struct DrainBarrier
+    marker::Vector{UInt8}
+    remaining::Int
+    done::Channel{Nothing}
+end
+
+const active_drain_barrier = Ref{Union{Nothing, DrainBarrier}}(nothing)
+const drain_marker_counter = Ref{UInt}(0)
 
 function json_parse(s::String)
     chars = collect(s)
@@ -274,17 +284,155 @@ function emit_frame(frame)
     end
 end
 
-function drain_stream(rd, kind)
+function find_subsequence(haystack::Vector{UInt8}, needle::Vector{UInt8})
+    needle_len = length(needle)
+    if needle_len == 0 || length(haystack) < needle_len
+        return nothing
+    end
+    last_start = length(haystack) - needle_len + 1
+    for start in 1:last_start
+        matched = true
+        @inbounds for offset in 1:needle_len
+            if haystack[start + offset - 1] != needle[offset]
+                matched = false
+                break
+            end
+        end
+        if matched
+            return start
+        end
+    end
+    return nothing
+end
+
+function marker_overlap(haystack::Vector{UInt8}, needle::Vector{UInt8})
+    max_overlap = min(length(haystack), length(needle) - 1)
+    for overlap in max_overlap:-1:1
+        matched = true
+        @inbounds for offset in 1:overlap
+            if haystack[length(haystack) - overlap + offset] != needle[offset]
+                matched = false
+                break
+            end
+        end
+        if matched
+            return overlap
+        end
+    end
+    return 0
+end
+
+function emit_stream_bytes(kind, bytes::Vector{UInt8})
+    rid = current_rid
+    if rid === nothing || isempty(bytes)
+        return
+    end
+    emit_frame(Dict("type" => kind, "id" => rid, "data" => String(copy(bytes))))
+end
+
+function signal_drain_barrier!(marker::Vector{UInt8})
+    done_channel = lock(drain_state_lock) do
+        barrier = active_drain_barrier[]
+        if barrier === nothing || barrier.marker != marker
+            return nothing
+        end
+        barrier.remaining -= 1
+        if barrier.remaining == 0
+            active_drain_barrier[] = nothing
+            return barrier.done
+        end
+        return nothing
+    end
+    if done_channel !== nothing
+        put!(done_channel, nothing)
+    end
+    return nothing
+end
+
+function process_stream_buffer!(buffer::Vector{UInt8}, kind; flush_all::Bool=false)
+    while true
+        barrier = lock(drain_state_lock) do
+            active_drain_barrier[]
+        end
+        marker = barrier === nothing ? nothing : barrier.marker
+        if marker === nothing
+            if !isempty(buffer)
+                emit_stream_bytes(kind, buffer)
+                empty!(buffer)
+            end
+            return
+        end
+
+        marker_index = find_subsequence(buffer, marker)
+        if marker_index !== nothing
+            emit_len = marker_index - 1
+            if emit_len > 0
+                emit_stream_bytes(kind, buffer[1:emit_len])
+            end
+            deleteat!(buffer, 1:(marker_index + length(marker) - 1))
+            signal_drain_barrier!(marker)
+            continue
+        end
+
+        keep_len = flush_all ? 0 : marker_overlap(buffer, marker)
+        emit_len = length(buffer) - keep_len
+        if emit_len > 0
+            emit_stream_bytes(kind, buffer[1:emit_len])
+            deleteat!(buffer, 1:emit_len)
+        end
+        return
+    end
+end
+
+function next_drain_marker()
+    drain_marker_counter[] += UInt(1)
+    return Vector{UInt8}(codeunits("\0__OMP_DRAIN__:" * string(drain_marker_counter[]) * ":" * string(time_ns()) * "\0"))
+end
+
+function await_stream_drains()
+    flush(stdout)
+    flush(stderr)
+    barrier = DrainBarrier(next_drain_marker(), 2, Channel{Nothing}(1))
+    lock(drain_state_lock) do
+        if active_drain_barrier[] !== nothing
+            error("Drain barrier already active")
+        end
+        active_drain_barrier[] = barrier
+    end
     try
-        while !eof(rd)
-            line = readline(rd, keep=true)
-            rid = current_rid
-            if rid !== nothing && !isempty(line)
-                emit_frame(Dict("type" => kind, "id" => rid, "data" => line))
+        Base.write(out_wr, barrier.marker)
+        flush(out_wr)
+        Base.write(err_wr, barrier.marker)
+        flush(err_wr)
+        take!(barrier.done)
+    finally
+        lock(drain_state_lock) do
+            if active_drain_barrier[] === barrier
+                active_drain_barrier[] = nothing
+            end
+        end
+    end
+    return nothing
+end
+
+function drain_stream(rd, kind)
+    buffer = UInt8[]
+    try
+        while true
+            data = readavailable(rd)
+            if !isempty(data)
+                append!(buffer, data)
+                process_stream_buffer!(buffer, kind)
+            elseif eof(rd)
+                break
+            else
+                sleep(0.001)
             end
         end
     catch
         # ignore
+    finally
+        process_stream_buffer!(buffer, kind, flush_all=true)
     end
 end
 
@@ -469,11 +617,7 @@ function main()
                 emit_error(rid, err, catch_backtrace())
             end
             
-            # Flush stdout and stderr writes before sending done frame
-            flush(stdout)
-            flush(stderr)
-            # Yield to make sure async drain processes all writes
-            sleep(0.01)
+            await_stream_drains()
             
             emit_frame(Dict(
                 "type" => "done",
diff --git a/packages/coding-agent/src/eval/rb/executor.ts b/packages/coding-agent/src/eval/rb/executor.ts
index aeedbf966..cfaceeef0 100644
--- a/packages/coding-agent/src/eval/rb/executor.ts
+++ b/packages/coding-agent/src/eval/rb/executor.ts
@@ -98,17 +98,24 @@ export interface RubyResult {
 // register against the same tuple; the kernel stays alive until the last owner detaches.
 // ---------------------------------------------------------------------------
 
-interface RubySession {
-	sessionKey: string;
-	sessionId: string;
-	cwd: string;
-	kernel: RubyKernel;
+interface RubySessionOwners {
 	ownerIds: Set<string>;
 	hasFallbackOwner: boolean;
 }
 
+interface RubySession extends RubySessionOwners {
+	sessionKey: string;
+	sessionId: string;
+	cwd: string;
+	kernel: RubyKernel;
+}
+
+interface StartingRubySession extends RubySessionOwners {
+	promise: Promise<RubySession>;
+}
+
 const sessions = new Map<string, RubySession>();
-const startingSessions = new Map<string, Promise<RubySession>>();
+const startingSessions = new Map<string, StartingRubySession>();
 const resettingSessions = new Map<string, Promise<void>>();
 
 function normalizeSessionCwd(cwd: string): string {
@@ -317,7 +324,7 @@ async function startKernel(cwd: string, options: RubyExecutorOptions): Promise<R
 	});
 }
 
-function attachOwner(session: RubySession, sessionId: string, ownerId: string | undefined): void {
+function attachOwner(session: RubySessionOwners, sessionId: string, ownerId: string | undefined): void {
 	if (ownerId !== undefined) {
 		if (session.hasFallbackOwner) {
 			session.ownerIds.delete(sessionId);
@@ -345,10 +352,10 @@ async function acquireSession(
 	}
 	const starting = startingSessions.get(sessionKey);
 	if (starting) {
-		const session = await starting;
-		attachOwner(session, sessionId, options.kernelOwnerId);
-		return session;
+		attachOwner(starting, sessionId, options.kernelOwnerId);
+		return await starting.promise;
 	}
+	let startingSession!: StartingRubySession;
 	const startup = (async () => {
 		const kernel = await startKernel(cwd, options);
 		const session: RubySession = {
@@ -356,19 +363,25 @@ async function acquireSession(
 			sessionId,
 			cwd,
 			kernel,
-			ownerIds: new Set(),
-			hasFallbackOwner: false,
+			ownerIds: new Set(startingSession.ownerIds),
+			hasFallbackOwner: startingSession.hasFallbackOwner,
 		};
-		sessions.set(sessionKey, session);
+		if (startingSessions.get(sessionKey) === startingSession) {
+			sessions.set(sessionKey, session);
+		}
 		return session;
 	})();
-	startingSessions.set(sessionKey, startup);
+	startingSession = {
+		ownerIds: new Set(),
+		hasFallbackOwner: false,
+		promise: startup,
+	};
+	attachOwner(startingSession, sessionId, options.kernelOwnerId);
+	startingSessions.set(sessionKey, startingSession);
 	try {
-		const session = await startup;
-		attachOwner(session, sessionId, options.kernelOwnerId);
-		return session;
+		return await startup;
 	} finally {
-		if (startingSessions.get(sessionKey) === startup) startingSessions.delete(sessionKey);
+		if (startingSessions.get(sessionKey) === startingSession) startingSessions.delete(sessionKey);
 	}
 }
 
@@ -391,7 +404,8 @@ async function replaceSessionKernel(session: RubySession, cwd: string, options:
 }
 
 async function resetSession(sessionKey: string): Promise<void> {
-	const existing = sessions.get(sessionKey) ?? (await startingSessions.get(sessionKey)?.catch(() => undefined));
+	const existing =
+		sessions.get(sessionKey) ?? (await startingSessions.get(sessionKey)?.promise.catch(() => undefined));
 	if (!existing) return;
 	sessions.delete(sessionKey);
 	await existing.kernel.shutdown().catch(() => undefined);
@@ -402,7 +416,7 @@ async function resetSession(sessionKey: string): Promise<void> {
 // ---------------------------------------------------------------------------
 
 export async function disposeAllRubyKernelSessions(): Promise<void> {
-	const pending = [...startingSessions.values()];
+	const pending = [...startingSessions.values()].map(starting => starting.promise);
 	startingSessions.clear();
 	const started = await Promise.allSettled(pending);
 	const all = [...sessions.entries()];
@@ -433,6 +447,7 @@ export async function disposeAllRubyKernelSessions(): Promise<void> {
 
 export async function disposeRubyKernelSessionsByOwner(ownerId: string): Promise<void> {
 	const toShutdown: RubySession[] = [];
+	const startingToShutdown: StartingRubySession[] = [];
 	for (const session of [...sessions.values()]) {
 		if (!session.ownerIds.has(ownerId)) continue;
 		if (session.ownerIds.size === 1) {
@@ -441,9 +456,25 @@ export async function disposeRubyKernelSessionsByOwner(ownerId: string): Promise
 		}
 		session.ownerIds.delete(ownerId);
 	}
+	for (const [sessionKey, starting] of [...startingSessions.entries()]) {
+		if (sessions.has(sessionKey) || !starting.ownerIds.has(ownerId)) continue;
+		if (starting.ownerIds.size === 1) {
+			startingSessions.delete(sessionKey);
+			startingToShutdown.push(starting);
+			continue;
+		}
+		starting.ownerIds.delete(ownerId);
+	}
 	for (const session of toShutdown) {
 		if (sessions.get(session.sessionKey) === session) sessions.delete(session.sessionKey);
 	}
+	const started = await Promise.allSettled(startingToShutdown.map(starting => starting.promise));
+	for (const result of started) {
+		if (result.status !== "fulfilled") continue;
+		const session = result.value;
+		if (sessions.get(session.sessionKey) === session) sessions.delete(session.sessionKey);
+		toShutdown.push(session);
+	}
 	const results = await Promise.allSettled(toShutdown.map(session => session.kernel.shutdown()));
 	for (let i = 0; i < toShutdown.length; i += 1) {
 		const session = toShutdown[i];
diff --git a/packages/coding-agent/src/eval/rb/kernel.ts b/packages/coding-agent/src/eval/rb/kernel.ts
index b00b0a472..ed0664148 100644
--- a/packages/coding-agent/src/eval/rb/kernel.ts
+++ b/packages/coding-agent/src/eval/rb/kernel.ts
@@ -334,8 +334,13 @@ export class RubyKernel {
 			});
 		};
 
+		let requestWritten = false;
 		const requestCancel = () => {
 			if (pending.settled || pending.escalationTimer) return;
+			if (!requestWritten) {
+				finalize();
+				return;
+			}
 			void this.interrupt();
 			const escalation = setTimeout(() => {
 				if (pending.settled) return;
@@ -375,6 +380,10 @@ export class RubyKernel {
 				onAbort();
 			} else {
 				options.signal.addEventListener("abort", onAbort, { once: true });
+				if (options.signal.aborted) {
+					options.signal.removeEventListener("abort", onAbort);
+					onAbort();
+				}
 			}
 		}
 
@@ -389,6 +398,11 @@ export class RubyKernel {
 			storeHistory: options?.storeHistory ?? !(options?.silent ?? false),
 		});
 
+		if (pending.settled) {
+			return promise;
+		}
+
+		requestWritten = true;
 		try {
 			await this.#writeLine(payload);
 		} catch (err) {
diff --git a/packages/coding-agent/src/eval/rb/runner.rb b/packages/coding-agent/src/eval/rb/runner.rb
index 9fa80d616..cc497d292 100644
--- a/packages/coding-agent/src/eval/rb/runner.rb
+++ b/packages/coding-agent/src/eval/rb/runner.rb
@@ -16,9 +16,9 @@
 # auto-displayed (like IRB) unless it is nil, an assignment, or a definition.
 #
 # Frame channel isolation: the original stdout is dup'd onto a private IO for
-# protocol frames, then fd 1 is repointed at an internal pipe. Child processes
-# that inherit fd 1 (any `system`/backtick call) land in that pipe and a drain
-# thread re-emits their bytes as stdout frames instead of corrupting the NDJSON
+# protocol frames, then fd 1/fd 2 are repointed at internal pipes. Child
+# processes that inherit stdout/stderr land in those pipes and drain threads
+# re-emit their bytes as stdout/stderr frames instead of corrupting the NDJSON
 # channel. Ruby-level writes go through $stdout/$stderr proxies that emit frames
 # synchronously so they order correctly with display output.
 
@@ -39,15 +39,25 @@ $__omp_silent = false
 begin
   $__omp_frame_io = STDOUT.dup
   $__omp_frame_io.sync = true
-  __omp_cap_r, __omp_cap_w = IO.pipe
-  STDOUT.reopen(__omp_cap_w)
+  __omp_stdout_cap_r, __omp_stdout_cap_w = IO.pipe
+  STDOUT.reopen(__omp_stdout_cap_w)
   STDOUT.sync = true
-  __omp_cap_w.close
-  $__omp_capture_read = __omp_cap_r
+  __omp_stdout_cap_w.close
+  $__omp_stdout_capture_read = __omp_stdout_cap_r
 rescue StandardError
   $__omp_frame_io = STDOUT
   ($__omp_frame_io.sync = true) rescue nil
-  $__omp_capture_read = nil
+  $__omp_stdout_capture_read = nil
+end
+
+begin
+  __omp_stderr_cap_r, __omp_stderr_cap_w = IO.pipe
+  STDERR.reopen(__omp_stderr_cap_w)
+  STDERR.sync = true
+  __omp_stderr_cap_w.close
+  $__omp_stderr_capture_read = __omp_stderr_cap_r
+rescue StandardError
+  $__omp_stderr_capture_read = nil
 end
 
 # Protect the protocol channel from user code: read requests on a private dup of
@@ -159,8 +169,10 @@ end
 # ---------------------------------------------------------------------------
 
 class OmpStreamProxy
-  def initialize(kind)
+  def initialize(kind, io, fileno)
     @kind = kind
+    @io = io
+    @fileno = fileno
   end
 
   def write(*args)
@@ -214,19 +226,20 @@ class OmpStreamProxy
   def sync=(value); value; end
   def tty?; false; end
   def isatty; false; end
-  def fileno; 1; end
-  def to_io; STDOUT; end
+  def fileno; @fileno; end
+  def to_io; @io; end
   def closed?; false; end
   def fsync; 0; end
-  def external_encoding; Encoding::UTF_8; end
+  def external_encoding
+    (@io.external_encoding rescue Encoding::UTF_8)
+  end
 end
 
 # ---------------------------------------------------------------------------
-# fd-1 capture drain (child-process stdout) + parent watchdog
+# fd-1/fd-2 capture drains (child-process stdout/stderr) + parent watchdog
 # ---------------------------------------------------------------------------
 
-def __omp_start_capture_drain
-  io = $__omp_capture_read
+def __omp_start_capture_drain(io, kind)
   return if io.nil?
   Thread.new do
     loop do
@@ -243,7 +256,7 @@ def __omp_start_capture_drain
       if rid.nil?
         ($__omp_raw_stderr.write(chunk) rescue nil)
       else
-        __omp_emit("type" => "stdout", "id" => rid, "data" => __omp_scrub(chunk))
+        __omp_emit("type" => kind, "id" => rid, "data" => __omp_scrub(chunk))
       end
     end
   end
@@ -430,11 +443,12 @@ end
 # ---------------------------------------------------------------------------
 
 def __omp_main
-  $stdout = OmpStreamProxy.new("stdout")
-  $stderr = OmpStreamProxy.new("stderr")
+  $stdout = OmpStreamProxy.new("stdout", STDOUT, 1)
+  $stderr = OmpStreamProxy.new("stderr", STDERR, 2)
   __omp_install_idle_sigint
   __omp_start_parent_watchdog
-  __omp_start_capture_drain
+  __omp_start_capture_drain($__omp_stdout_capture_read, "stdout")
+  __omp_start_capture_drain($__omp_stderr_capture_read, "stderr")
 
   $__omp_proto_stdin.each_line do |raw|
     line = raw.strip
diff --git a/packages/coding-agent/src/eval/types.ts b/packages/coding-agent/src/eval/types.ts
index df22ccf0b..2463ada07 100644
--- a/packages/coding-agent/src/eval/types.ts
+++ b/packages/coding-agent/src/eval/types.ts
@@ -4,13 +4,13 @@ export type EvalLanguage = "python" | "js" | "ruby" | "julia";
 import type { ImageContent } from "@oh-my-pi/pi-ai";
 import type { OutputMeta } from "../tools/output-meta";
 
-/** Status event emitted by prelude helpers (python or js) for TUI rendering. */
+/** Status event emitted by eval prelude helpers for TUI rendering. */
 export interface EvalStatusEvent {
 	op: string;
 	[key: string]: unknown;
 }
 
-/** Display output captured during eval execution. Union of python and js shapes. */
+/** Display output captured during eval execution across supported backends. */
 export type EvalDisplayOutput =
 	| { type: "json"; data: unknown }
 	| { type: "image"; data: string; mimeType: string }
diff --git a/packages/coding-agent/src/modes/theme/theme.ts b/packages/coding-agent/src/modes/theme/theme.ts
index 9b39345e9..ca5879223 100644
--- a/packages/coding-agent/src/modes/theme/theme.ts
+++ b/packages/coding-agent/src/modes/theme/theme.ts
@@ -169,6 +169,7 @@ export type SymbolKey =
 	| "lang.cpp"
 	| "lang.csharp"
 	| "lang.ruby"
+	| "lang.julia"
 	| "lang.php"
 	| "lang.swift"
 	| "lang.kotlin"
@@ -369,6 +370,7 @@ const UNICODE_SYMBOLS: SymbolMap = {
 	"lang.cpp": "➕",
 	"lang.csharp": "♯",
 	"lang.ruby": "💎",
+	"lang.julia": "Ⓙ",
 	"lang.php": "🐘",
 	"lang.swift": "🕊",
 	"lang.kotlin": "🅺",
@@ -673,6 +675,7 @@ const NERD_SYMBOLS: SymbolMap = {
 	"lang.cpp": "\u{E61D}",
 	"lang.csharp": "\u{E7BC}",
 	"lang.ruby": "\u{E791}",
+	"lang.julia": "\u{E624}",
 	"lang.php": "\u{E608}",
 	"lang.swift": "\u{E755}",
 	"lang.kotlin": "\u{E634}",
@@ -870,6 +873,7 @@ const ASCII_SYMBOLS: SymbolMap = {
 	"lang.cpp": "cpp",
 	"lang.csharp": "cs",
 	"lang.ruby": "rb",
+	"lang.julia": "jl",
 	"lang.php": "php",
 	"lang.swift": "swift",
 	"lang.kotlin": "kt",
@@ -1335,6 +1339,8 @@ const langMap: Record<string, SymbolKey> = {
 	cs: "lang.csharp",
 	ruby: "lang.ruby",
 	rb: "lang.ruby",
+	julia: "lang.julia",
+	jl: "lang.julia",
 	php: "lang.php",
 	swift: "lang.swift",
 	kotlin: "lang.kotlin",
@@ -1406,6 +1412,20 @@ const langMap: Record<string, SymbolKey> = {
 	bin: "lang.binary",
 };
 
+/**
+ * Brand colors for language icons, keyed by the resolved `lang.*` SymbolKey.
+ * Used by {@link Theme.getLangIconStyled} so eval-kernel cell headers tint each
+ * language with its recognizable hue (JS yellow, Ruby red, Julia purple, Python
+ * blue) instead of a flat muted gray. Applied as truecolor/256 per the active
+ * color mode; languages without an entry fall back to the muted theme color.
+ */
+const LANG_BRAND_COLORS: Partial<Record<SymbolKey, string>> = {
+	"lang.javascript": "#f7df1e",
+	"lang.python": "#3776ab",
+	"lang.ruby": "#cc342d",
+	"lang.julia": "#9558b2",
+};
+
 /**
  * Resolve a theme color value (hex string or 256-color index) to a CSS hex string.
  * Empty string represents the default terminal color.
@@ -1874,6 +1894,21 @@ export class Theme {
 		const key = langMap[normalized];
 		return key ? this.#symbols[key] : this.#symbols["lang.default"];
 	}
+
+	/**
+	 * Language icon tinted with the language's brand color (see
+	 * {@link LANG_BRAND_COLORS}). Falls back to the muted theme color for
+	 * languages without a brand entry, and returns the bare (possibly empty)
+	 * icon when the active symbol preset has none.
+	 */
+	getLangIconStyled(lang: string | undefined): string {
+		const icon = this.getLangIcon(lang);
+		if (!icon) return icon;
+		const key = lang ? langMap[lang.toLowerCase()] : undefined;
+		const hex = key ? LANG_BRAND_COLORS[key] : undefined;
+		if (!hex) return this.fg("muted", icon);
+		return `${colorToAnsi(hex, this.mode)}${icon}\x1b[39m`;
+	}
 }
 
 // ============================================================================
diff --git a/packages/coding-agent/src/modes/utils/copy-targets.ts b/packages/coding-agent/src/modes/utils/copy-targets.ts
index b93c9129f..3eb0bdce0 100644
--- a/packages/coding-agent/src/modes/utils/copy-targets.ts
+++ b/packages/coding-agent/src/modes/utils/copy-targets.ts
@@ -22,7 +22,7 @@ export type MessageBlock = ({ kind: "code" } & CodeBlock) | ({ kind: "quote" } &
 export interface LastCommand {
 	kind: "bash" | "eval";
 	code: string;
-	/** Highlight language: "bash" for bash, "python"/"javascript" for eval. */
+	/** Highlight language: "bash" for bash, or the resolved eval language ("python"/"javascript"/"ruby"/"julia"). */
 	language: string;
 }
 
diff --git a/packages/coding-agent/src/sdk.ts b/packages/coding-agent/src/sdk.ts
index acc71956f..8b57ac801 100644
--- a/packages/coding-agent/src/sdk.ts
+++ b/packages/coding-agent/src/sdk.ts
@@ -474,7 +474,7 @@ export interface CreateAgentSessionOptions {
 
 	/** Enable LSP integration (tool, formatting, diagnostics, warmup). Default: true */
 	enableLsp?: boolean;
-	/** Skip Python kernel availability check and prelude warmup */
+	/** Skip subprocess-kernel availability checks and prelude warmup */
 	skipPythonPreflight?: boolean;
 	/** Tool names explicitly requested (enables disabled-by-default tools) */
 	toolNames?: string[];
@@ -868,11 +868,11 @@ function registerSshCleanup(): void {
 	postmortem.register("ssh-cleanup", cleanupSshResources);
 }
 
-let pythonCleanupRegistered = false;
+let evalCleanupRegistered = false;
 
-function registerPythonCleanup(): void {
-	if (pythonCleanupRegistered) return;
-	pythonCleanupRegistered = true;
+function registerEvalCleanup(): void {
+	if (evalCleanupRegistered) return;
+	evalCleanupRegistered = true;
 	postmortem.register("python-cleanup", disposeAllKernelSessions);
 	postmortem.register("ruby-cleanup", disposeAllRubyKernelSessions);
 	postmortem.register("julia-cleanup", disposeAllJuliaKernelSessions);
@@ -1084,7 +1084,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 	const eventBus = options.eventBus ?? new EventBus();
 
 	registerSshCleanup();
-	registerPythonCleanup();
+	registerEvalCleanup();
 
 	// Pin authStorage to modelRegistry.authStorage: ModelRegistry.getApiKey() routes refresh
 	// failures through that instance, so any divergent storage handed to the bridge / mcpManager
@@ -2697,7 +2697,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 			const originalDispose = session.dispose.bind(session);
 			session.dispose = async () => {
 				try {
-					// Reject new session work (Python/eval starts) the moment disposal
+					// Reject new session work (eval starts) the moment disposal
 					// begins — the lifecycle await below opens an async gap before
 					// AgentSession.dispose() would otherwise set its guards.
 					session.beginDispose();
diff --git a/packages/coding-agent/src/session/agent-session.ts b/packages/coding-agent/src/session/agent-session.ts
index a2061f4b8..b25b30507 100644
--- a/packages/coding-agent/src/session/agent-session.ts
+++ b/packages/coding-agent/src/session/agent-session.ts
@@ -522,7 +522,7 @@ export interface AgentSessionConfig {
 	obfuscator?: SecretObfuscator;
 	/** Inherited eval executor session id from a parent agent. */
 	parentEvalSessionId?: string;
-	/** Logical owner for retained Python kernels created by this session. */
+	/** Logical owner for retained eval kernels created by this session. */
 	evalKernelOwnerId?: string;
 	/**
 	 * AsyncJobManager that this session installed as the process-global instance.
@@ -4175,7 +4175,7 @@ export class AgentSession {
 
 	/**
 	 * Synchronously mark the session as disposing so new work is rejected
-	 * immediately: Python/eval starts throw, queued asides are dropped, and the
+	 * immediately: eval starts throw, queued asides are dropped, and the
 	 * aside provider is detached. Idempotent; `dispose()` runs it first.
 	 *
 	 * Wrappers that await other teardown before delegating to `dispose()` MUST
@@ -4237,11 +4237,9 @@ export class AgentSession {
 				AsyncJobManager.setInstance(undefined);
 			}
 		}
-		const pythonExecutionsSettled = await this.#prepareEvalExecutionsForDispose();
-		if (!pythonExecutionsSettled) {
-			logger.warn(
-				"Detaching retained Python kernel ownership during dispose while Python execution is still active",
-			);
+		const evalExecutionsSettled = await this.#prepareEvalExecutionsForDispose();
+		if (!evalExecutionsSettled) {
+			logger.warn("Detaching retained eval-kernel ownership during dispose while eval execution is still active");
 		}
 		await disposeKernelSessionsByOwner(this.#evalKernelOwnerId);
 		await disposeRubyKernelSessionsByOwner(this.#evalKernelOwnerId);
diff --git a/packages/coding-agent/src/task/executor.ts b/packages/coding-agent/src/task/executor.ts
index cd10f7433..6837f5d10 100644
--- a/packages/coding-agent/src/task/executor.ts
+++ b/packages/coding-agent/src/task/executor.ts
@@ -41,7 +41,8 @@ import type { AuthStorage } from "../session/auth-storage";
 import { SKILL_PROMPT_MESSAGE_TYPE, USER_INTERRUPT_LABEL } from "../session/messages";
 import { SessionManager } from "../session/session-manager";
 import { truncateTail } from "../session/streaming-output";
-import type { ContextFileEntry } from "../tools";
+import type { ContextFileEntry, ToolSession } from "../tools";
+import { resolveEvalBackends } from "../tools/eval-backends";
 import { isIrcEnabled } from "../tools/irc";
 import { normalizeSchema } from "../tools/jtd-to-json-schema";
 import {
@@ -1790,12 +1791,9 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 		toolNames = [...toolNames, "irc"];
 	}
 	if (toolNames?.includes("exec")) {
-		const allowEvalPy = settings.get("eval.py") ?? true;
-		const allowEvalJs = settings.get("eval.js") ?? true;
-		const allowEvalRb = settings.get("eval.rb") ?? true;
-		const allowEvalJl = settings.get("eval.jl") ?? true;
+		const backends = resolveEvalBackends({ settings } as ToolSession);
 		const expanded = toolNames.filter(name => name !== "exec");
-		if (allowEvalPy || allowEvalJs || allowEvalRb || allowEvalJl) expanded.push("eval");
+		if (backends.python || backends.js || backends.ruby || backends.julia) expanded.push("eval");
 		expanded.push("bash");
 		toolNames = Array.from(new Set(expanded));
 	}
diff --git a/packages/coding-agent/src/tools/eval-backends.ts b/packages/coding-agent/src/tools/eval-backends.ts
index 81f808a2f..5888eee6e 100644
--- a/packages/coding-agent/src/tools/eval-backends.ts
+++ b/packages/coding-agent/src/tools/eval-backends.ts
@@ -19,8 +19,9 @@ export function readEvalBackendsAllowance(session: ToolSession): EvalBackendsAll
 }
 
 /**
- * Materialize the active eval backend allowance: PI_PY / PI_JS / PI_RB env flags
- * override the per-key settings; otherwise settings (defaults true) win.
+ * Materialize the active eval backend allowance: PI_PY / PI_JS / PI_RB / PI_JL
+ * env flags override the per-key settings; otherwise settings (defaults true)
+ * win.
  */
 export function resolveEvalBackends(session: ToolSession): EvalBackendsAllowance {
 	const settings = readEvalBackendsAllowance(session);
diff --git a/packages/coding-agent/src/tools/eval-render.ts b/packages/coding-agent/src/tools/eval-render.ts
index 98221e503..293b2cd7f 100644
--- a/packages/coding-agent/src/tools/eval-render.ts
+++ b/packages/coding-agent/src/tools/eval-render.ts
@@ -2,11 +2,12 @@
  * TUI rendering for the eval tool.
  *
  * Split out from `eval.ts` so the renderer can be imported by `renderers.ts`
- * without dragging the eval *runtime* (JS/Python backends -> agent bridge ->
- * task executor -> sdk -> extension loader -> root barrel) into the renderer
- * module graph. That transitive chain re-enters `renderers.ts` while `eval.ts`
- * is still initializing, which previously crashed module load with a TDZ
- * `Cannot access 'evalToolRenderer' before initialization`.
+ * without dragging the eval *runtime* (JS/Python/Ruby/Julia backends ->
+ * agent bridge -> task executor -> sdk -> extension loader -> root barrel)
+ * into the renderer module graph. That transitive chain re-enters
+ * `renderers.ts` while `eval.ts` is still initializing, which previously
+ * crashed module load with a TDZ `Cannot access 'evalToolRenderer' before
+ * initialization`.
  */
 import type { Component } from "@oh-my-pi/pi-tui";
 import { Markdown, Text } from "@oh-my-pi/pi-tui";
@@ -512,6 +513,7 @@ export const evalToolRenderer = {
 						{
 							code: cell.code,
 							language: languageForHighlighter(cell.language),
+							showLanguage: true,
 							index: i,
 							total: cells.length,
 							title: cell.title,
@@ -614,6 +616,7 @@ export const evalToolRenderer = {
 							{
 								code: cell.code,
 								language: languageForHighlighter(cell.language ?? details?.language),
+								showLanguage: true,
 								index: i,
 								total: cellResults.length,
 								title: cell.title,
diff --git a/packages/coding-agent/src/tools/eval.ts b/packages/coding-agent/src/tools/eval.ts
index 75acb19af..d161c718c 100644
--- a/packages/coding-agent/src/tools/eval.ts
+++ b/packages/coding-agent/src/tools/eval.ts
@@ -31,7 +31,9 @@ const evalCellSchema = type({
 	language: type("'py' | 'js' | 'rb' | 'jl'").describe(
 		'runtime: "py" for the IPython kernel, "js" for the persistent JS VM, "rb" for the persistent Ruby kernel, "jl" for the persistent Julia kernel',
 	),
-	code: type("string").describe("cell body, verbatim. Top-level `await` is available in py/js."),
+	code: type("string").describe(
+		"cell body, verbatim. Top-level `await` is available in py/js; rb/jl auto-display the last expression like a REPL.",
+	),
 	"title?": type("string").describe('short label shown in transcript (e.g. "imports", "load config")'),
 	"timeout?": type("number").describe("per-cell timeout in seconds"),
 	"reset?": type("boolean").describe(
@@ -149,12 +151,18 @@ async function resolveBackend(session: ToolSession, language: EvalLanguage): Pro
 	const allowPy = backends.python;
 	const allowJs = backends.js;
 	const allowRb = backends.ruby;
+	const allowJl = backends.julia;
 
 	if (language === "python") {
 		if (!allowPy) throw new ToolError("Python backend is disabled (PI_PY=0 or eval.py = false).");
 		if (!(await pythonBackend.isAvailable(session))) {
+			const alternatives = [allowJs ? '"js"' : null, allowRb ? '"rb"' : null, allowJl ? '"jl"' : null].filter(
+				Boolean,
+			);
 			throw new ToolError(
-				'Python backend is unavailable in this session. Pass language: "js" or install the python kernel.',
+				alternatives.length > 0
+					? `Python backend is unavailable in this session. Pass language: ${alternatives.join(" or ")} or install the python kernel.`
+					: 'Python backend is unavailable in this session. Install the python kernel to use language: "py".',
 			);
 		}
 		return { backend: pythonBackend };
@@ -162,20 +170,41 @@ async function resolveBackend(session: ToolSession, language: EvalLanguage): Pro
 	if (language === "ruby") {
 		if (!allowRb) throw new ToolError("Ruby backend is disabled (PI_RB=0 or eval.rb = false).");
 		if (!(await rubyBackend.isAvailable(session))) {
-			throw new ToolError('Ruby backend is unavailable in this session. Pass language: "js" or install Ruby.');
+			const alternatives = [allowJs ? '"js"' : null, allowPy ? '"py"' : null, allowJl ? '"jl"' : null].filter(
+				Boolean,
+			);
+			throw new ToolError(
+				alternatives.length > 0
+					? `Ruby backend is unavailable in this session. Pass language: ${alternatives.join(" or ")} or install Ruby.`
+					: 'Ruby backend is unavailable in this session. Install Ruby to use language: "rb".',
+			);
 		}
 		return { backend: rubyBackend };
 	}
 	if (language === "julia") {
-		if (!backends.julia) throw new ToolError("Julia backend is disabled (PI_JL=0 or eval.jl = false).");
+		if (!allowJl) throw new ToolError("Julia backend is disabled (PI_JL=0 or eval.jl = false).");
 		if (!(await juliaBackend.isAvailable(session))) {
-			throw new ToolError('Julia backend is unavailable in this session. Pass language: "js" or install Julia.');
+			const alternatives = [allowJs ? '"js"' : null, allowPy ? '"py"' : null, allowRb ? '"rb"' : null].filter(
+				Boolean,
+			);
+			throw new ToolError(
+				alternatives.length > 0
+					? `Julia backend is unavailable in this session. Pass language: ${alternatives.join(" or ")} or install Julia.`
+					: 'Julia backend is unavailable in this session. Install Julia to use language: "jl".',
+			);
 		}
 		return { backend: juliaBackend };
 	}
 	if (!allowJs) throw new ToolError("JavaScript backend is disabled (PI_JS=0 or eval.js = false).");
 	return { backend: jsBackend };
 }
+function formatEvalInputLanguage(value: string): string {
+	if (value === "py" || value === "python") return "python";
+	if (value === "js" || value === "javascript") return "javascript";
+	if (value === "rb" || value === "ruby") return "ruby";
+	if (value === "jl" || value === "julia") return "julia";
+	return value;
+}
 
 export class EvalTool implements AgentTool<typeof evalSchema> {
 	readonly name = "eval";
@@ -185,7 +214,8 @@ export class EvalTool implements AgentTool<typeof evalSchema> {
 		const cells = Array.isArray(params.cells) ? params.cells : [];
 		const firstCell = cells[0] as Partial<EvalCellInput> | undefined;
 		if (!firstCell) return [];
-		const language = typeof firstCell.language === "string" ? firstCell.language : "(missing)";
+		const language =
+			typeof firstCell.language === "string" ? formatEvalInputLanguage(firstCell.language) : "javascript (default)";
 		const code = typeof firstCell.code === "string" ? firstCell.code : "";
 		const lines = [`Language: ${language}`, `Code:\n${truncateForPrompt(code)}`];
 		if (cells.length > 1) {
@@ -236,7 +266,7 @@ export class EvalTool implements AgentTool<typeof evalSchema> {
 		const first = cells.find(c => c && typeof c === "object");
 		if (!first) return "evaluating";
 		const title = typeof first.title === "string" ? first.title : undefined;
-		const language = typeof first.language === "string" ? first.language : "?";
+		const language = typeof first.language === "string" ? formatEvalInputLanguage(first.language) : "javascript";
 		const label = title || `running ${language}`;
 		return cells.length > 1 ? `${label} (+${cells.length - 1})` : label;
 	};
@@ -382,7 +412,7 @@ export class EvalTool implements AgentTool<typeof evalSchema> {
 					// The per-cell `timeout` is a budget on the cell runtime's *own*
 					// work. Host-side `agent()`/`parallel()`/`completion()` bridge calls suspend
 					// that budget entirely and restart a fresh timeout window when control
-					// returns to Python/JS. Compute, stdout, `log()`/`phase()`, and
+					// returns to the active backend runtime. Compute, stdout, `log()`/`phase()`, and
 					// ordinary tool calls all count against the budget. The watchdog drives
 					// `combinedSignal`; we pass no wall-clock deadline downstream so the
 					// backends never arm a competing fixed timer.
diff --git a/packages/coding-agent/src/tools/index.ts b/packages/coding-agent/src/tools/index.ts
index 9f83f9ae5..2eb00921e 100644
--- a/packages/coding-agent/src/tools/index.ts
+++ b/packages/coding-agent/src/tools/index.ts
@@ -167,7 +167,7 @@ export interface ToolSession {
 	suppressSpawnAdvisory?: boolean;
 	/** Optional fetch implementation injected into the URL read pipeline (tests, proxies). Defaults to global fetch. */
 	fetch?: FetchImpl;
-	/** Skip Python kernel availability check and warmup */
+	/** Skip subprocess-kernel availability checks and warmup */
 	skipPythonPreflight?: boolean;
 	/** Pre-loaded context files (AGENTS.md, etc) */
 	contextFiles?: ContextFileEntry[];
@@ -204,13 +204,13 @@ export interface ToolSession {
 	requireYieldTool?: boolean;
 	/** Task recursion depth (0 = top-level, 1 = first child, etc.) */
 	taskDepth?: number;
-	/** Get shared eval executor session ID. Subagents inherit this to share JS/Python state. */
+	/** Get shared eval executor session ID. Subagents inherit this to share JS/Python/Ruby/Julia state. */
 	getEvalSessionId?: () => string | null;
 	/** Get session file */
 	getSessionFile: () => string | null;
 	/** Get eval kernel owner ID for session-scoped retained-kernel cleanup. */
 	getEvalKernelOwnerId?: () => string | null;
-	/** Reject new eval (python or js) work once session disposal has started. */
+	/** Reject new eval work once session disposal has started. */
 	assertEvalExecutionAllowed?: () => void;
 	/** Track tool-owned eval work so session disposal can await/abort it like direct session eval runs. */
 	trackEvalExecution?<T>(execution: Promise<T>, abortController: AbortController): Promise<T>;
diff --git a/packages/coding-agent/src/tui/code-cell.ts b/packages/coding-agent/src/tui/code-cell.ts
index e269a9276..143e78f3d 100644
--- a/packages/coding-agent/src/tui/code-cell.ts
+++ b/packages/coding-agent/src/tui/code-cell.ts
@@ -32,6 +32,13 @@ export interface CodeCellOptions {
 	 */
 	codeTail?: boolean;
 	expanded?: boolean;
+	/**
+	 * Prefix the header with the cell's language icon (resolved through the
+	 * active symbol preset: nerd-font devicon, unicode emoji, or ascii
+	 * shorthand). Opt-in so only the eval kernel renderer labels each cell;
+	 * read/write/browser code cells stay icon-free.
+	 */
+	showLanguage?: boolean;
 	width: number;
 	codeStartLine?: number;
 	codeLineNumbers?: Array<number | null>;
@@ -47,8 +54,12 @@ function getState(status?: CodeCellOptions["status"]): State | undefined {
 }
 
 function formatHeader(options: CodeCellOptions, theme: Theme): { title: string; meta?: string } {
-	const { index, total, title, status, spinnerFrame, duration } = options;
+	const { index, total, title, status, spinnerFrame, duration, language, showLanguage } = options;
 	const parts: string[] = [];
+	if (showLanguage && language) {
+		const langIcon = theme.getLangIconStyled(language);
+		if (langIcon) parts.push(langIcon);
+	}
 	if (status) {
 		const icon = formatStatusIcon(
 			status === "complete"
diff --git a/packages/coding-agent/test/core/ruby-runner.integration.test.ts b/packages/coding-agent/test/core/ruby-runner.integration.test.ts
index ea6b29741..c7ccd1fa4 100644
--- a/packages/coding-agent/test/core/ruby-runner.integration.test.ts
+++ b/packages/coding-agent/test/core/ruby-runner.integration.test.ts
@@ -85,6 +85,29 @@ describe.skipIf(!SHOULD_RUN)("ruby runner subprocess", () => {
 		}
 	});
 
+	it("does not write an already-aborted request and keeps the kernel usable", async () => {
+		using tempDir = TempDir.createSync("@ruby-runner-preabort-");
+		const kernel = await RubyKernel.start({ cwd: tempDir.path() });
+		try {
+			const controller = new AbortController();
+			controller.abort();
+			const cancelled = await executeRubyWithKernel(kernel, 'File.write("aborted.txt", "nope")', {
+				signal: controller.signal,
+			});
+			expect(cancelled.cancelled).toBe(true);
+
+			const sideEffect = await executeRubyWithKernel(kernel, 'File.exist?("aborted.txt")', {});
+			expect(sideEffect.exitCode).toBe(0);
+			expect(sideEffect.output).toContain("false");
+
+			const after = await executeRubyWithKernel(kernel, "20 + 22", {});
+			expect(after.exitCode).toBe(0);
+			expect(after.output).toContain("42");
+		} finally {
+			await kernel.shutdown();
+		}
+	});
+
 	it("surfaces Ruby errors with a non-zero exit and the message", async () => {
 		using tempDir = TempDir.createSync("@ruby-runner-error-");
 		const kernel = await RubyKernel.start({ cwd: tempDir.path() });
@@ -97,6 +120,30 @@ describe.skipIf(!SHOULD_RUN)("ruby runner subprocess", () => {
 		}
 	});
 
+	it("surfaces Ruby and child-process stderr in output", async () => {
+		using tempDir = TempDir.createSync("@ruby-runner-stderr-");
+		const kernel = await RubyKernel.start({ cwd: tempDir.path() });
+		try {
+			const result = await executeRubyWithKernel(
+				kernel,
+				[
+					'$stderr.print("ruby stderr\\n")',
+					'STDERR.print("constant stderr\\n")',
+					'require "rbconfig"',
+					'system(RbConfig.ruby, "-e", \'STDERR.print("child stderr\\\\n"); STDOUT.print("child stdout\\\\n")\')',
+				].join("\n"),
+				{},
+			);
+			expect(result.exitCode).toBe(0);
+			expect(result.output).toContain("ruby stderr\n");
+			expect(result.output).toContain("constant stderr\n");
+			expect(result.output).toContain("child stderr\n");
+			expect(result.output).toContain("child stdout\n");
+		} finally {
+			await kernel.shutdown();
+		}
+	});
+
 	it("exposes prelude file + text helpers", async () => {
 		using tempDir = TempDir.createSync("@ruby-runner-prelude-");
 		const kernel = await RubyKernel.start({ cwd: tempDir.path() });