diff --git a/docs/task-agent-discovery.md b/docs/task-agent-discovery.md
index cb1dcde6e..4ce802152 100644
--- a/docs/task-agent-discovery.md
+++ b/docs/task-agent-discovery.md
@@ -45,7 +45,7 @@ Bundled agents are embedded at build time (`src/task/agents.ts`) using text impo
 `EMBEDDED_AGENT_DEFS` defines:
 
 - `scout`, `designer`, `reviewer`, `librarian` from prompt files
-- `task` and `sonic` from shared `task.md` body plus injected frontmatter; `task` ships with `prewalk: true` (default hand-off to the `smol` role, opt out per agent via `/agents` / `task.agentPrewalk`)
+- `task` and `sonic` from shared `task.md` body plus injected frontmatter; no bundled agent sets `prewalk` — the generic `task` agent's hand-off is armed by the `task.prewalk` setting (default off), or per agent via `/agents` / `task.agentPrewalk` / user agent frontmatter
 
 Loading path:
 
diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 43a2fbfc4..0f287b0e4 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -12,8 +12,8 @@
 ### Added
 
 - Added the `edit.enforceSeenLines` setting (default off) to gate the hashline seen-line guard. When off, hashline tags validate on content hash alone and any anchor into the tagged content applies; when on, edits anchored on lines a prior `read`/`grep` never displayed are rejected.
-- Added per-agent prewalk for subagents: a `prewalk` frontmatter field (`true` = hand off to the default prewalk target, a string = custom target model pattern) and a `task.agentPrewalk` settings override toggled per agent from the `/agents` dashboard with `P`. The bundled generic `task` agent ships with prewalk enabled by default (skipped when the target resolves to the subagent's own starting model, and never armed for plan-mode spawns). Prewalk-armed subagents keep the normally parent-owned `todo` tool so the plan-nudge → todo → hand-off flow works, and the prewalk todo gate now keys on the active tool set instead of the registry so a deactivated todo tool can no longer stall the switch.
-- Added `xd://` virtual tool devices (setting `tools.xdev`, default on): built-ins declaring `loadMode: "discoverable"` (browser, debug, lsp, ast_grep/ast_edit, github, web_search, ...) are unmounted from the request's tools array entirely and driven through the tools the model already has: `read xd://` lists mounted devices, `read xd://<tool>` returns docs + JSON schema, and `write xd://<tool>` with a JSON args object as content executes the tool. Args validate against the mounted tool's real schema (returned on mismatch), and the tools array (and prompt-cache prefix) never changes shape when devices mount or unmount mid-session. `todo`, `ask`, and `grep` stay top-level for their harness integrations; `/tools` lists mounted devices; and `xd://` writes render with the mounted tool's own TUI renderer — streamed call previews draw nothing until the path is provably not an `xd://` device, then forward the incrementally decoded JSON content as live inner args. Explicit `--tools read,...,xdev` lists opt lean sets into the same mounting; `tools.discoveryMode: "all"` takes precedence when active. Full docs + JSON schema for every mounted device are inlined into the system prompt's `xd://` section, so no discovery `read` is required before first use; `read xd://<tool>` remains available for on-demand re-fetch.
+- Added per-agent prewalk for subagents: a `prewalk` frontmatter field (`true` = hand off to the default prewalk target, a string = custom target model pattern), a `task.agentPrewalk` settings override toggled per agent from the `/agents` dashboard with `P`, and a `task.prewalk` boolean (default off) that arms the bundled generic `task` agent. Prewalk is opt-in everywhere (when armed, it is skipped if the target resolves to the subagent's own starting model, and never armed for plan-mode spawns). Prewalk-armed subagents keep the normally parent-owned `todo` tool so the plan-nudge → todo → hand-off flow works, and the prewalk todo gate now keys on the active tool set instead of the registry so a deactivated todo tool can no longer stall the switch.
+- Added `xd://` virtual tool devices (setting `tools.xdev`, default on): mounted tools are discovered via `read xd://`, documented by `read xd://<tool>`, and executed by `write xd://<tool>`, with compact prompt docs plus on-demand doc fetch for overflowed devices
 
 ### Changed
 
@@ -23,6 +23,9 @@
 - Changed every bundled TTSR rule to warn without interrupting generation.
 - Renamed the system prompt's project-context section wrapper from `<context>` to `<repo-rules>` to stop it colliding with the `task` tool's `context` parameter under in-band XML tool dialects: models were closing `<parameter name="context">` with a stray `</context>` (primed by the ambient section tag) and emitting sibling params as bare `<tasks>` elements, so `tasks` arrived missing.
 - Rendered `read xd://` calls in the compact grouped read view instead of a full tool-execution card; other internal URLs (`skill://`, `agent://`, …) still render full so their resolved content stays visible.
+- `--tools` now rejects unknown tool names with a usage error instead of logging to the log file and silently narrowing the toolset (e.g. a stale `--tools bash,ssh` after the ssh tool's removal ran with just bash).
+- Capped the xd:// device docs inlined into the system prompt: full docs + schema inline in catalog order up to a 48k-char budget (10k per device); devices past the caps are listed by name + summary and fetched on demand via `read xd://<tool>`, so large MCP catalogs no longer bloat every request.
+- Legacy BM25-discovery settings keys are migrated instead of silently ignored: `tools.discoveryMode: "off"` maps to `tools.xdev: false` (everything mounts top-level), and the dead `tools.discoveryMode` / `tools.essentialOverride` / `mcp.discoveryMode` / `mcp.discoveryDefaultServers` keys are removed from config.
 
 ### Removed
 
@@ -42,6 +45,8 @@
 - Fixed the Bash tool hanging when in-process commands read process substitution operands such as `<(cmd)` ([#5557](https://github.com/can1357/oh-my-pi/issues/5557)).
 - Fixed `/share` and `/export` web views rendering inline Markdown inside list items as literal text ([#5567](https://github.com/can1357/oh-my-pi/issues/5567)).
 - Fixed plan-mode re-entry dropping a new plan request when a prior plan artifact existed: the re-entry prompt led with the old plan and contradicted the plan-file guidance, so weak models only reconciled the incomplete previous plan. Re-entry now anchors on the new request and folds any old-plan corrections into it ([#5576](https://github.com/can1357/oh-my-pi/issues/5576)).
+- Fixed ACP clients rendering `xd://` device dispatches as file edits: a `write xd://<tool>` now maps to an `execute`-kind tool call titled with the device URL, and scheme-qualified subjects (`xd://`, `skill://`, …) no longer fabricate editor locations like `/repo/xd:/github`.
+- Fixed non-yolo approval modes double-prompting for `xd://` device dispatches: the write tool's outer gate resolves approval at the mounted tool's tier, and the inner per-tool gate no longer re-prompts for the same action (explicit `tools.approval.<tool>` prompt/deny policies still apply).
 
 ## [16.5.2] - 2026-07-14
 
diff --git a/packages/coding-agent/DEVELOPMENT.md b/packages/coding-agent/DEVELOPMENT.md
index ae4c3d2d4..17ae8360b 100644
--- a/packages/coding-agent/DEVELOPMENT.md
+++ b/packages/coding-agent/DEVELOPMENT.md
@@ -107,17 +107,16 @@ Top-level entry modules: `cli.ts`, `main.ts`, `sdk.ts`, `index.ts` (SDK barrel),
 - Authoring + registry: [custom-tools.md](../../docs/custom-tools.md)
 - Output/artifacts: [blob-artifact-architecture.md](../../docs/blob-artifact-architecture.md)
 - Gating/approval: [approval-mode.md](../../docs/approval-mode.md), [resolve-tool-runtime.md](../../docs/resolve-tool-runtime.md)
-- Per-tool reference: [`docs/tools/`](../../docs/tools/) — `read`, `write`, `edit`, `ast-edit`, `ast-grep`, `search`, `find`, `bash`, `eval`, `job`, `lsp`, `debug`, `task`, `irc`, `web_search`, `browser`, `github`, `ssh`, `inspect_image`, `ask`, `todo`, `recall`, `retain`, `reflect`, `checkpoint`, `rewind`
+- Per-tool reference: [`docs/tools/`](../../docs/tools/) — `read`, `write`, `edit`, `ast-edit`, `ast-grep`, `grep`, `glob`, `bash`, `eval`, `hub`, `lsp`, `debug`, `task`, `web_search`, `browser`, `github`, `inspect_image`, `ask`, `todo`, `recall`, `retain`, `reflect`, `checkpoint`, `rewind`
 
 ### Execution backends
 - [bash-tool-runtime.md](../../docs/bash-tool-runtime.md), [tools/bash.md](../../docs/tools/bash.md)
-- [python-repl.md](../../docs/python-repl.md), [notebook-tool-runtime.md](../../docs/notebook-tool-runtime.md), [tools/eval.md](../../docs/tools/eval.md), [tools/job.md](../../docs/tools/job.md)
-- [tools/ssh.md](../../docs/tools/ssh.md)
+- [python-repl.md](../../docs/python-repl.md), [notebook-tool-runtime.md](../../docs/notebook-tool-runtime.md), [tools/eval.md](../../docs/tools/eval.md), [tools/hub.md](../../docs/tools/hub.md)
 - [tools/debug.md](../../docs/tools/debug.md), [tools/lsp.md](../../docs/tools/lsp.md), [lsp-config.md](../../docs/lsp-config.md)
 
 ### Task delegation and subagents
 - [task-agent-discovery.md](../../docs/task-agent-discovery.md), [tools/task.md](../../docs/tools/task.md)
-- [collab.md](../../docs/collab.md), [tools/irc.md](../../docs/tools/irc.md)
+- [collab.md](../../docs/collab.md), [tools/hub.md](../../docs/tools/hub.md)
 
 ### Web I/O and retrieval
 - [tools/web_search.md](../../docs/tools/web_search.md), [tools/browser.md](../../docs/tools/browser.md), [tools/github.md](../../docs/tools/github.md)
diff --git a/packages/coding-agent/src/cli/flag-tables.ts b/packages/coding-agent/src/cli/flag-tables.ts
index 60752c1c9..a4c28d271 100644
--- a/packages/coding-agent/src/cli/flag-tables.ts
+++ b/packages/coding-agent/src/cli/flag-tables.ts
@@ -177,18 +177,16 @@ export const STRING_SETTERS: Record<string, StringSetter> = {
 				.map(s => s.trim())
 				.filter(Boolean),
 		);
-		const valid: string[] = [];
-		for (const name of names) {
-			if (deps.builtinToolNames.includes(name)) {
-				valid.push(name);
-			} else {
-				deps.logger.warn("Unknown tool passed to --tools", {
-					tool: name,
-					validTools: deps.builtinToolNames,
-				});
-			}
+		// An unknown name silently narrowing the toolset is worse than a failed
+		// launch: scripts keep running believing the tool is available (e.g. a
+		// stale `--tools bash,ssh` after the ssh tool's removal).
+		const unknown = names.filter(name => !deps.builtinToolNames.includes(name));
+		if (unknown.length > 0) {
+			throw new CliUsageError(
+				`Unknown tool${unknown.length === 1 ? "" : "s"} in --tools: ${unknown.join(", ")}. Valid tools: ${deps.builtinToolNames.join(", ")}.`,
+			);
 		}
-		result.tools = valid;
+		result.tools = names;
 	},
 	"--thinking": (result, value, deps) => {
 		const thinking = deps.parseThinking(value);
diff --git a/packages/coding-agent/src/config/settings-schema.ts b/packages/coding-agent/src/config/settings-schema.ts
index 67be5cacc..57da8814f 100644
--- a/packages/coding-agent/src/config/settings-schema.ts
+++ b/packages/coding-agent/src/config/settings-schema.ts
@@ -4256,6 +4256,17 @@ export const SETTINGS_SCHEMA = {
 		type: "record",
 		default: {} as Record<string, string>,
 	},
+	"task.prewalk": {
+		type: "boolean",
+		default: false,
+		ui: {
+			tab: "tools",
+			group: "Subagents",
+			label: "Generic Task Prewalk",
+			description:
+				"Arm prewalk for the bundled generic `task` subagent: it starts on its resolved model, plans and begins the implementation, then hands off to the 'smol' role at its first edit/write. Per-agent overrides (task.agentPrewalk, toggled with P in /agents) and user agent `prewalk` frontmatter apply regardless of this toggle.",
+		},
+	},
 
 	"tasks.todoClearDelay": {
 		type: "number",
diff --git a/packages/coding-agent/src/config/settings.ts b/packages/coding-agent/src/config/settings.ts
index fdf661edb..dc52ddd52 100644
--- a/packages/coding-agent/src/config/settings.ts
+++ b/packages/coding-agent/src/config/settings.ts
@@ -1253,6 +1253,33 @@ export class Settings {
 		if (tierTouched) raw.tier = tierObj;
 		delete raw.fastModeScope;
 
+		// BM25 tool discovery removal: tools.discoveryMode / tools.essentialOverride /
+		// mcp.discoveryMode / mcp.discoveryDefaultServers are gone. The one intent
+		// worth carrying over is discoveryMode "off" ("no discovery layer, every
+		// tool ships top-level"), whose modern equivalent is disabling the xd://
+		// transport; the other values map to the default (xdev on). Dead keys are
+		// deleted so they stop lingering in config.yml.
+		const toolsObj = raw.tools as Record<string, unknown> | undefined;
+		const legacyDiscoveryMode = toolsObj?.discoveryMode ?? raw["tools.discoveryMode"];
+		if (legacyDiscoveryMode === "off" && toolsObj?.xdev === undefined && raw["tools.xdev"] === undefined) {
+			const toolsRoot = toolsObj ?? {};
+			toolsRoot.xdev = false;
+			raw.tools = toolsRoot;
+		}
+		if (toolsObj) {
+			delete toolsObj.discoveryMode;
+			delete toolsObj.essentialOverride;
+		}
+		delete raw["tools.discoveryMode"];
+		delete raw["tools.essentialOverride"];
+		const mcpObj = raw.mcp as Record<string, unknown> | undefined;
+		if (mcpObj) {
+			delete mcpObj.discoveryMode;
+			delete mcpObj.discoveryDefaultServers;
+		}
+		delete raw["mcp.discoveryMode"];
+		delete raw["mcp.discoveryDefaultServers"];
+
 		return raw;
 	}
 
diff --git a/packages/coding-agent/src/extensibility/extensions/wrapper.ts b/packages/coding-agent/src/extensibility/extensions/wrapper.ts
index 32f740336..10cd980af 100644
--- a/packages/coding-agent/src/extensibility/extensions/wrapper.ts
+++ b/packages/coding-agent/src/extensibility/extensions/wrapper.ts
@@ -11,7 +11,7 @@ import type {
 import type { ImageContent, Static, TextContent, TSchema } from "@oh-my-pi/pi-ai";
 import type { Settings } from "../../config/settings";
 import type { Theme } from "../../modes/theme/theme";
-import { type ApprovalMode, formatApprovalPrompt, requiresApproval } from "../../tools/approval";
+import { type ApprovalMode, formatApprovalPrompt, resolveApproval } from "../../tools/approval";
 import { normalizeToolEventInput, resolveToolEventInput } from "../tool-event-input";
 import { applyToolProxy } from "../tool-proxy";
 import type { ExtensionRunner } from "./runner";
@@ -127,7 +127,21 @@ export class ExtensionToolWrapper<TParameters extends TSchema = TSchema, TDetail
 		const configuredMode = (settings?.get("tools.approvalMode") ?? "yolo") as ApprovalMode;
 		const approvalMode: ApprovalMode = cliAutoApprove ? "yolo" : configuredMode;
 		const userPolicies = (settings?.get("tools.approval") ?? {}) as Record<string, unknown>;
-		const approvalCheck = requiresApproval(this.tool, params, approvalMode, userPolicies);
+		const resolved = resolveApproval(this.tool, params, approvalMode, userPolicies);
+		if (resolved.policy === "deny") {
+			throw new Error(
+				`Tool "${this.tool.name}" is blocked by user policy.\n` +
+					`To allow: remove "tools.approval.${this.tool.name}: deny" from config.`,
+			);
+		}
+		// An xd:// device dispatch already cleared the write tool's outer gate at
+		// this tool's tier — re-prompting would double-ask for one action. Explicit
+		// per-tool "prompt" policies and tool-demanded overrides still prompt.
+		const explicitPrompt = resolved.override || Object.hasOwn(userPolicies, this.tool.name);
+		const approvalCheck = {
+			required: resolved.policy === "prompt" && (explicitPrompt || context?.xdevApproved !== true),
+			reason: resolved.reason,
+		};
 
 		if (approvalCheck.required) {
 			const hasApprovalHandlers =
diff --git a/packages/coding-agent/src/modes/acp/acp-event-mapper.ts b/packages/coding-agent/src/modes/acp/acp-event-mapper.ts
index f3536b598..fac1807f0 100644
--- a/packages/coding-agent/src/modes/acp/acp-event-mapper.ts
+++ b/packages/coding-agent/src/modes/acp/acp-event-mapper.ts
@@ -6,6 +6,7 @@ import type {
 	ToolCallLocation,
 	ToolKind,
 } from "@agentclientprotocol/sdk";
+import { parseXdUrl } from "../../internal-urls/xd-protocol";
 import type { AgentSessionEvent } from "../../session/agent-session";
 import { resolveToCwd } from "../../tools/path-utils";
 import type { TodoStatus } from "../../tools/todo";
@@ -128,7 +129,24 @@ interface TextMessageLike {
 
 const ACP_TEXT_LIMIT = 4_000;
 
-export function mapToolKind(toolName: string): ToolKind {
+/**
+ * Device name when the call is an `xd://` device dispatch riding the
+ * read/write transport (`write xd://<tool>` executes the mounted tool,
+ * `read xd://` is discovery). Returns `undefined` for plain file paths.
+ */
+function xdevDispatchDevice(toolName: string, args: unknown): string | undefined {
+	if (toolName !== "write" && toolName !== "read") return undefined;
+	const path = extractStringProperty<PathContainer>(args, "path");
+	if (!path) return undefined;
+	return parseXdUrl(path)?.name ?? undefined;
+}
+
+export function mapToolKind(toolName: string, args?: unknown): ToolKind {
+	// An xd:// device write executes the mounted tool — "edit" would make ACP
+	// clients render it as a file modification to a nonexistent path (and
+	// auto-approve it under edit-tier policies). Reads stay "read": listing
+	// devices or fetching docs is discovery.
+	if (toolName === "write" && xdevDispatchDevice(toolName, args)) return "execute";
 	switch (toolName) {
 		case "read":
 			return "read";
@@ -420,7 +438,7 @@ export function buildToolCallStartUpdate(input: {
 		sessionUpdate: "tool_call",
 		toolCallId: input.toolCallId,
 		title: buildToolTitle(input.toolName, input.args, input.intent),
-		kind: mapToolKind(input.toolName),
+		kind: mapToolKind(input.toolName, input.args),
 		status: input.status ?? "pending",
 		rawInput: input.args,
 	};
@@ -544,6 +562,9 @@ function buildToolTitle(toolName: string, args: unknown, intent: string | undefi
 		extractStringProperty<PatternContainer>(args, "pattern") ??
 		extractStringProperty<QueryContainer>(args, "query");
 	if (subject) {
+		// Internal URLs (xd://github, skill://react, …) name their target fully;
+		// prefixing the transport tool reads as a file write to a fake path.
+		if (INTERNAL_URL_SUBJECT.test(subject)) return subject;
 		return `${toolName}: ${subject}`;
 	}
 
@@ -565,11 +586,18 @@ function toAcpLocationPath(value: string, cwd?: string): string {
 	}
 }
 
+/**
+ * Scheme-qualified subjects (`xd://`, `skill://`, `agent://`, `https://`, …)
+ * are not local files: resolving them against cwd fabricates paths like
+ * `/repo/xd:/github` and makes editors focus nonexistent files.
+ */
+const INTERNAL_URL_SUBJECT = /^[a-z][a-z0-9+.-]*:\/\//i;
+
 function extractToolLocations(args: unknown, cwd?: string): ToolCallLocation[] {
 	const locations: ToolCallLocation[] = [];
 	const seen = new Set<string>();
 	const pushPath = (raw: string | undefined) => {
-		if (!raw) return;
+		if (!raw || INTERNAL_URL_SUBJECT.test(raw)) return;
 		const path = toAcpLocationPath(raw, cwd);
 		if (seen.has(path)) return;
 		seen.add(path);
diff --git a/packages/coding-agent/src/modes/interactive-mode.ts b/packages/coding-agent/src/modes/interactive-mode.ts
index 5e39ddae6..e7a517c30 100644
--- a/packages/coding-agent/src/modes/interactive-mode.ts
+++ b/packages/coding-agent/src/modes/interactive-mode.ts
@@ -2220,12 +2220,12 @@ export class InteractiveMode implements InteractiveModeContext {
 		// `write` and refine it with `edit`, and plan approval itself is a `write`
 		// to `xd://propose`. Both must be in the active set or the agent falls
 		// back to `edit` on a non-existent file and stalls — and cannot submit the plan.
-		// `edit` is an essential built-in so it survives `tools.discoveryMode ===
-		// "all"`; re-activate `write` here only when the current registry entry is
-		// the built-in write tool (issue #3165). A shadowing extension tool named
-		// `write` must stay inactive because plan mode's read-only guarantee relies
-		// on the built-in write/edit guard. The standing handler below consumes
-		// plan-approval dispatches.
+		// `edit` is an essential built-in and always ships top-level; re-activate
+		// `write` here only when the current registry entry is the built-in write
+		// tool (issue #3165). A shadowing extension tool named `write` must stay
+		// inactive because plan mode's read-only guarantee relies on the built-in
+		// write/edit guard. The standing handler below consumes plan-approval
+		// dispatches.
 		const planAugmentations: string[] = [];
 		if (this.session.hasBuiltInTool("write")) {
 			planAugmentations.push("write");
diff --git a/packages/coding-agent/src/session/agent-session.ts b/packages/coding-agent/src/session/agent-session.ts
index e6f6904cd..d82507381 100644
--- a/packages/coding-agent/src/session/agent-session.ts
+++ b/packages/coding-agent/src/session/agent-session.ts
@@ -1737,6 +1737,8 @@ export class AgentSession {
 	#prewalk: Prewalk | undefined;
 	/** True once the plan nudge has been queued; scrubbed from context at the switch. */
 	#prewalkPlanInjected = false;
+	/** Armed by plan/tool progress; consumed by one text-only continuation. */
+	#prewalkContinuePending = false;
 	/** True once any successful `todo` call landed — opens the prewalk
 	 *  trigger gate: the switch fires at the first edit/write AFTER the todo
 	 *  list exists (sessions without an ACTIVE todo tool skip the gate). */
@@ -2230,15 +2232,24 @@ export class AgentSession {
 		const prewalk = this.#prewalk;
 		if (!prewalk || context?.message.role !== "assistant") return;
 
-		// Structural safety net: every branch below assumes the agent loop will
-		// run another turn. It won't if THIS turn had no tool calls — the loop
-		// treats a text-only turn as "the agent is done" and ends the session
-		// with no further prompting. The plan nudge explicitly asks for a prose
-		// reply, which makes a text-only turn common right after it — observed
+		const todoCalledThisTurn = context.toolResults.some(result => result.toolName === "todo");
+		if (todoCalledThisTurn) {
+			this.#prewalkTodoSeen = true;
+		}
+
+		// The plan nudge asks for a prose plan before implementation begins,
+		// but the agent loop treats each text-only reply as terminal — observed
 		// silently killing production SWE-bench runs before any code was ever
-		// written. Force one more turn only in that specific, self-created
-		// hazard window.
-		if (this.#prewalkPlanInjected && context.toolResults.length === 0) {
+		// written. Tool progress re-arms one continuation, allowing split flows
+		// such as plan → todo → prose → read → prose → edit/write. Consuming the
+		// arm before steering also detects completion: two consecutive text-only
+		// replies have no intervening progress, so the second ends naturally
+		// instead of producing the #5551 loop.
+		const hasToolResults = context.toolResults.length > 0;
+		if (this.#prewalkPlanInjected && hasToolResults) {
+			this.#prewalkContinuePending = true;
+		} else if (this.#prewalkContinuePending) {
+			this.#prewalkContinuePending = false;
 			this.agent.steer({
 				role: "custom",
 				customType: PREWALK_CONTINUE_MESSAGE_TYPE,
@@ -2264,6 +2275,7 @@ export class AgentSession {
 		if (!action) {
 			if (!this.#prewalkPlanInjected) {
 				this.#prewalkPlanInjected = true;
+				this.#prewalkContinuePending = true;
 				this.agent.steer({
 					role: "custom",
 					customType: PREWALK_PLAN_MESSAGE_TYPE,
@@ -2324,6 +2336,7 @@ export class AgentSession {
 		}
 		this.#prewalk = { target, thinkingLevel };
 		this.#prewalkPlanInjected = true;
+		this.#prewalkContinuePending = true;
 		this.agent.steer({
 			role: "custom",
 			customType: PREWALK_PLAN_MESSAGE_TYPE,
@@ -11656,9 +11669,9 @@ export class AgentSession {
 			}
 		}
 
-		// Must check the active tool set, not just the registry: tool discovery
-		// (tools.discoveryMode === "all") can register `todo` while hiding it from
-		// the exposed tools. Forcing a named tool_choice for an inactive tool makes
+		// Must check the active tool set, not just the registry: a registered
+		// tool can be hidden from the exposed tools (e.g. unmounted under the
+		// xd:// transport). Forcing a named tool_choice for an inactive tool makes
 		// the provider reject the request (HTTP 400).
 		if (!this.getActiveToolNames().includes("todo")) {
 			logger.warn("Eager todo enforcement skipped because todo is not active", {
diff --git a/packages/coding-agent/src/task/agents.ts b/packages/coding-agent/src/task/agents.ts
index 40aade7f0..30a811901 100644
--- a/packages/coding-agent/src/task/agents.ts
+++ b/packages/coding-agent/src/task/agents.ts
@@ -53,9 +53,10 @@ const EMBEDDED_AGENT_DEFS: EmbeddedAgentDef[] = [
 			spawns: "*",
 			model: "@task",
 			thinkingLevel: AUTO_THINKING,
-			// Strong model plans and starts the implementation, then hands off to
-			// the smol role. Per-agent opt-out via /agents (task.agentPrewalk).
-			prewalk: true,
+			// No `prewalk` frontmatter: the generic task hand-off (strong model
+			// plans, then hands off to the smol role) is armed by the
+			// `task.prewalk` setting (default off) or per agent via /agents
+			// (task.agentPrewalk).
 		},
 		template: taskMd,
 	},
diff --git a/packages/coding-agent/src/task/executor.ts b/packages/coding-agent/src/task/executor.ts
index 1df404352..9a541dddf 100644
--- a/packages/coding-agent/src/task/executor.ts
+++ b/packages/coding-agent/src/task/executor.ts
@@ -2309,12 +2309,15 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 			// Per-agent prewalk: the agent definition's `prewalk` frontmatter or the
 			// `task.agentPrewalk` settings override hands the subagent off to a
 			// fast/cheap target at its first edit/write — the same mechanism as the
-			// session-level --prewalk. Resolution failures skip prewalk instead of
-			// failing the spawn.
+			// session-level --prewalk. The bundled generic `task` agent has no
+			// frontmatter default; the `task.prewalk` toggle (default off) arms it.
+			// Resolution failures skip prewalk instead of failing the spawn.
 			let prewalk: Prewalk | undefined;
+			const genericTaskPrewalk =
+				agent.source === "bundled" && agent.name === "task" && settings.get("task.prewalk") ? true : undefined;
 			const prewalkPattern = resolveAgentPrewalkPattern({
 				settingsOverride: settings.get("task.agentPrewalk")[agent.name],
-				agentPrewalk: agent.prewalk,
+				agentPrewalk: agent.prewalk ?? genericTaskPrewalk,
 			});
 			if (prewalkPattern) {
 				const resolvedPrewalk = resolveModelOverride([prewalkPattern], modelRegistry, settings);
diff --git a/packages/coding-agent/src/tools/context.ts b/packages/coding-agent/src/tools/context.ts
index 9e9d61924..e785df631 100644
--- a/packages/coding-agent/src/tools/context.ts
+++ b/packages/coding-agent/src/tools/context.ts
@@ -8,6 +8,11 @@ declare module "@oh-my-pi/pi-agent-core" {
 		hasUI?: boolean;
 		toolNames?: string[];
 		toolCall?: ToolCallContext;
+		/** Set on `xd://` device dispatches: the write tool's outer approval gate
+		 *  already resolved this call at the mounted tool's tier, so the inner
+		 *  wrapper must not re-prompt for the same action (explicit per-tool
+		 *  policies and overrides still apply). */
+		xdevApproved?: boolean;
 	}
 }
 
diff --git a/packages/coding-agent/src/tools/write.ts b/packages/coding-agent/src/tools/write.ts
index 856eea986..811356099 100644
--- a/packages/coding-agent/src/tools/write.ts
+++ b/packages/coding-agent/src/tools/write.ts
@@ -1019,7 +1019,10 @@ export class WriteTool implements AgentTool<typeof writeSchema, WriteToolDetails
 									_toolCallId,
 									signal,
 									onUpdate as AgentToolUpdateCallback,
-									context,
+									// The write tool's own gate just resolved approval at this
+									// device's tier (see #approval above) — mark it so a wrapped
+									// inner tool does not prompt a second time.
+									context ? { ...context, xdevApproved: true } : undefined,
 								);
 								xdResult = {
 									content: result.content,
diff --git a/packages/coding-agent/src/tools/xdev.ts b/packages/coding-agent/src/tools/xdev.ts
index bc496272a..0cdab8c91 100644
--- a/packages/coding-agent/src/tools/xdev.ts
+++ b/packages/coding-agent/src/tools/xdev.ts
@@ -227,11 +227,47 @@ export class XdevRegistry {
 		return renderDocs(this.#resolve(name));
 	}
 
-	/** Full docs + schema for every mounted device, nested under a `##` heading for system-prompt embedding. */
+	/**
+	 * Char budget for the full docs inlined into the system prompt. Large MCP
+	 * catalogs previously shipped every schema top-level; without a cap they
+	 * would bloat every request. Devices past the budget fall back to a
+	 * one-line summary — their docs stay one `read xd://<tool>` away.
+	 */
+	static readonly DOCS_TOTAL_BUDGET = 48_000;
+	/** A single device's docs above this size never inline: one pathological
+	 *  MCP description must not starve every later device. */
+	static readonly DOCS_PER_DEVICE_CAP = 10_000;
+
+	/**
+	 * Docs + schema for mounted devices, nested under `##` headings for
+	 * system-prompt embedding. Inlines full docs in catalog order (built-ins
+	 * first) until {@link DOCS_TOTAL_BUDGET} is spent; the rest are listed by
+	 * name + summary with a pointer to on-demand `read xd://<tool>` docs.
+	 */
 	docsAll(): string {
-		return this.list()
-			.map(tool => renderDocs(tool, "##"))
-			.join("\n\n");
+		const sections: string[] = [];
+		const overflow: Tool[] = [];
+		let used = 0;
+		for (const tool of this.list()) {
+			const docs = renderDocs(tool, "##");
+			if (docs.length > XdevRegistry.DOCS_PER_DEVICE_CAP || used + docs.length > XdevRegistry.DOCS_TOTAL_BUDGET) {
+				overflow.push(tool);
+				continue;
+			}
+			used += docs.length;
+			sections.push(docs);
+		}
+		if (overflow.length > 0) {
+			sections.push(
+				[
+					"## Additional devices (docs on demand)",
+					...overflow.map(tool => `- ${XD_URL_PREFIX}${tool.name} — ${toolSummary(tool)}`),
+					"",
+					`Read ${XD_URL_PREFIX}<tool> for full docs + JSON schema before first use.`,
+				].join("\n"),
+			);
+		}
+		return sections.join("\n\n");
 	}
 
 	#resolve(name: string): Tool {
diff --git a/packages/coding-agent/test/acp-event-mapper.test.ts b/packages/coding-agent/test/acp-event-mapper.test.ts
index d72639b58..7d184987c 100644
--- a/packages/coding-agent/test/acp-event-mapper.test.ts
+++ b/packages/coding-agent/test/acp-event-mapper.test.ts
@@ -991,6 +991,45 @@ describe("ACP event mapper", () => {
 		expect(update.locations).toEqual([{ path: "src/current.ts" }, { path: "src/old.ts" }, { path: "src/new.ts" }]);
 	});
 
+	it("maps xd:// device writes to an execute call with no fabricated file location", () => {
+		const update = buildToolCallStartUpdate({
+			toolCallId: "toolu_xd_write",
+			toolName: "write",
+			args: { path: "xd://github", content: '{"op":"repo_view"}' },
+			cwd: path.resolve("/repo"),
+		});
+
+		expectAcpStructure(arkSessionNotification, { sessionId: "session-1", update });
+		expect(update).toMatchObject({
+			sessionUpdate: "tool_call",
+			title: "xd://github",
+			kind: "execute",
+		});
+		expect("locations" in update).toBe(false);
+	});
+
+	it("keeps xd:// discovery reads as read kind and plain file writes as edit", () => {
+		const discovery = buildToolCallStartUpdate({
+			toolCallId: "toolu_xd_read",
+			toolName: "read",
+			args: { path: "xd://lsp" },
+		});
+		expect(discovery).toMatchObject({ title: "xd://lsp", kind: "read" });
+		expect("locations" in discovery).toBe(false);
+
+		const fileWrite = buildToolCallStartUpdate({
+			toolCallId: "toolu_file_write",
+			toolName: "write",
+			args: { path: "src/foo.ts", content: "x" },
+			cwd: path.resolve("/repo"),
+		});
+		expect(fileWrite).toMatchObject({
+			title: "write: src/foo.ts",
+			kind: "edit",
+			locations: [{ path: path.resolve("/repo", "src/foo.ts") }],
+		});
+	});
+
 	it("rejects mutated ACP notification discriminators", () => {
 		const [notification] = mapAgentSessionEventToAcpSessionUpdates(
 			{
diff --git a/packages/coding-agent/test/flag-tables.test.ts b/packages/coding-agent/test/flag-tables.test.ts
index f59574c07..3a359bfd8 100644
--- a/packages/coding-agent/test/flag-tables.test.ts
+++ b/packages/coding-agent/test/flag-tables.test.ts
@@ -62,6 +62,14 @@ describe("--tools legacy aliases", () => {
 
 		expect(result.tools).toEqual(["grep", "glob"]);
 	});
+
+	it("rejects unknown tool names instead of silently narrowing the toolset", () => {
+		// Removed tools (ssh, job, irc, launch, search_tool_bm25) used to be
+		// dropped with only a log-file warning, so `--tools bash,ssh` ran with
+		// just bash and no visible notice.
+		expect(() => parseArgs(["--tools", "bash,ssh"])).toThrow(CliUsageError);
+		expect(() => parseArgs(["--tools", "bash,ssh"])).toThrow(/Unknown tool in --tools: ssh/);
+	});
 });
 
 describe("OPTIONAL_FLAGS per-flag quirks", () => {
diff --git a/packages/coding-agent/test/settings-manager.test.ts b/packages/coding-agent/test/settings-manager.test.ts
index f47c2e38d..e6d1bd702 100644
--- a/packages/coding-agent/test/settings-manager.test.ts
+++ b/packages/coding-agent/test/settings-manager.test.ts
@@ -694,6 +694,27 @@ describe("Settings", () => {
 			expect(settings.get("grep.enabled")).toBe(true);
 		});
 
+		it("maps legacy tools.discoveryMode 'off' to tools.xdev false and drops dead discovery keys", async () => {
+			await writeSettings({
+				tools: { discoveryMode: "off", essentialOverride: ["read"] },
+				mcp: { discoveryMode: "auto", discoveryDefaultServers: ["gh"] },
+			});
+
+			const settings = await Settings.init({ cwd: projectDir, agentDir });
+
+			expect(settings.get("tools.xdev")).toBe(false);
+		});
+
+		it("keeps tools.xdev default for non-'off' legacy discovery modes and honors an explicit xdev", async () => {
+			await writeSettings({ tools: { discoveryMode: "auto" } });
+			const settings = await Settings.init({ cwd: projectDir, agentDir });
+			expect(settings.get("tools.xdev")).toBe(true);
+
+			await writeSettings({ tools: { discoveryMode: "off", xdev: true } });
+			const explicit = await Settings.init({ cwd: projectDir, agentDir });
+			expect(explicit.get("tools.xdev")).toBe(true);
+		});
+
 		it("migrates from settings.json containing comments", async () => {
 			const jsonPath = path.join(agentDir, "settings.json");
 			await fs.promises.writeFile(
diff --git a/packages/coding-agent/test/task/executor-prewalk.test.ts b/packages/coding-agent/test/task/executor-prewalk.test.ts
index bea38ca71..b2ef997d9 100644
--- a/packages/coding-agent/test/task/executor-prewalk.test.ts
+++ b/packages/coding-agent/test/task/executor-prewalk.test.ts
@@ -34,6 +34,8 @@ function yieldEmittingSession(initialTools: string[] = ["read", "yield"]): Agent
 		extensionRunner: undefined,
 		sessionManager: { appendSessionInit: () => {} },
 		getActiveToolNames: () => activeTools,
+		getEnabledToolNames: () => activeTools,
+		getAllToolNames: () => activeTools,
 		setActiveToolsByName: async (toolNames: string[]) => {
 			activeTools = toolNames;
 		},
@@ -192,6 +194,46 @@ describe("runSubprocess per-agent prewalk", () => {
 		expect(spy.mock.calls[0]?.[0]?.prewalk?.target.id).toBe(target.id);
 	});
 
+	it("task.prewalk arms the bundled generic task agent without frontmatter", async () => {
+		const settings = Settings.isolated();
+		settings.setModelRole("smol", `${target.provider}/${target.id}`);
+		settings.set("task.prewalk", true);
+		const spy = vi
+			.spyOn(sdkModule, "createAgentSession")
+			.mockResolvedValue(createSessionResult(yieldEmittingSession()));
+
+		const result = await runSubprocess({
+			...baseOptions("subagent-prewalk-setting-on", settings),
+			agent: { ...baseAgent, model: [`${primary.provider}/${primary.id}`] },
+		});
+
+		expect(result.exitCode).toBe(0);
+		expect(spy.mock.calls[0]?.[0]?.prewalk?.target.id).toBe(target.id);
+	});
+
+	it("task.prewalk defaults off and leaves other bundled agents alone when on", async () => {
+		const settings = Settings.isolated();
+		settings.setModelRole("smol", `${target.provider}/${target.id}`);
+		const spy = vi
+			.spyOn(sdkModule, "createAgentSession")
+			.mockResolvedValue(createSessionResult(yieldEmittingSession()));
+
+		const offByDefault = await runSubprocess({
+			...baseOptions("subagent-prewalk-setting-default", settings),
+			agent: { ...baseAgent, model: [`${primary.provider}/${primary.id}`] },
+		});
+		expect(offByDefault.exitCode).toBe(0);
+		expect(spy.mock.calls[0]?.[0]?.prewalk).toBeUndefined();
+
+		settings.set("task.prewalk", true);
+		const otherAgent = await runSubprocess({
+			...baseOptions("subagent-prewalk-setting-other-agent", settings),
+			agent: { ...baseAgent, name: "sonic", model: [`${primary.provider}/${primary.id}`] },
+		});
+		expect(otherAgent.exitCode).toBe(0);
+		expect(spy.mock.calls[1]?.[0]?.prewalk).toBeUndefined();
+	});
+
 	it("skips prewalk when the target resolves to the starting model", async () => {
 		const spy = vi
 			.spyOn(sdkModule, "createAgentSession")
diff --git a/packages/coding-agent/test/tools/approval-mode.test.ts b/packages/coding-agent/test/tools/approval-mode.test.ts
index 2b0af2767..f960762d6 100644
--- a/packages/coding-agent/test/tools/approval-mode.test.ts
+++ b/packages/coding-agent/test/tools/approval-mode.test.ts
@@ -180,6 +180,41 @@ describe("tools.approvalMode setting", () => {
 		expect(textOf(result)).toContain("(no output)");
 	});
 
+	it("xd:// dispatch approval (xdevApproved) suppresses the tier-only re-prompt", async () => {
+		// The write tool's outer gate already prompted at the device tool's tier;
+		// without the flag this exact call rejects (see the always-ask test above).
+		const settings = approvalSettings({ "tools.approvalMode": "always-ask" });
+		const result = await bashTool().execute("xdev-tier", { command: "echo dispatched" }, undefined, undefined, {
+			settings,
+			xdevApproved: true,
+		} as AgentToolContext);
+		expect(textOf(result)).toContain("dispatched");
+	});
+
+	it("xdevApproved does not bypass explicit per-tool prompt or deny policies", async () => {
+		const promptSettings = approvalSettings({
+			"tools.approvalMode": "always-ask",
+			"tools.approval": { bash: "prompt" },
+		});
+		await expect(
+			bashTool().execute("xdev-explicit-prompt", { command: "echo blocked" }, undefined, undefined, {
+				settings: promptSettings,
+				xdevApproved: true,
+			} as AgentToolContext),
+		).rejects.toThrow(/requires approval but no interactive UI available/);
+
+		const denySettings = approvalSettings({
+			"tools.approvalMode": "always-ask",
+			"tools.approval": { bash: "deny" },
+		});
+		await expect(
+			bashTool().execute("xdev-denied", { command: "echo blocked" }, undefined, undefined, {
+				settings: denySettings,
+				xdevApproved: true,
+			} as AgentToolContext),
+		).rejects.toThrow(/blocked by user policy/);
+	});
+
 	it("constructs an extensionRunner unconditionally so the approval gate is always installed", async () => {
 		// Regression lock for the architectural fix: the per-tool approval gate is implemented
 		// inside `ExtensionToolWrapper`, which is only attached when `session.extensionRunner` exists.
diff --git a/packages/coding-agent/test/tools/task-agent-capabilities.test.ts b/packages/coding-agent/test/tools/task-agent-capabilities.test.ts
index 574d6ed90..59d727e82 100644
--- a/packages/coding-agent/test/tools/task-agent-capabilities.test.ts
+++ b/packages/coding-agent/test/tools/task-agent-capabilities.test.ts
@@ -28,11 +28,10 @@ describe("task agent capability descriptions", () => {
 			expect(agentByName(agents, name).readSummarize).toBeUndefined();
 		}
 	});
-	it("ships the generic task agent with prewalk enabled, all other bundled agents without", () => {
+	it("ships every bundled agent without prewalk; hand-off is opt-in via task.agentPrewalk", () => {
 		const agents = loadBundledAgents();
 
-		expect(agentByName(agents, "task").prewalk).toBe(true);
-		for (const name of ["scout", "sonic", "reviewer", "designer", "librarian"]) {
+		for (const name of ["task", "scout", "sonic", "reviewer", "designer", "librarian"]) {
 			expect(agentByName(agents, name).prewalk).toBeUndefined();
 		}
 	});
diff --git a/packages/coding-agent/test/write-xdev-dispatch.test.ts b/packages/coding-agent/test/write-xdev-dispatch.test.ts
index e491ca708..7a405f070 100644
--- a/packages/coding-agent/test/write-xdev-dispatch.test.ts
+++ b/packages/coding-agent/test/write-xdev-dispatch.test.ts
@@ -7,6 +7,7 @@ import * as themeModule from "@oh-my-pi/pi-coding-agent/modes/theme/theme";
 import { ToolChoiceQueue } from "@oh-my-pi/pi-coding-agent/session/tool-choice-queue";
 import { createTools, type ToolSession } from "@oh-my-pi/pi-coding-agent/tools";
 import { writeToolRenderer } from "@oh-my-pi/pi-coding-agent/tools/write";
+import { XdevRegistry } from "@oh-my-pi/pi-coding-agent/tools/xdev";
 import { removeWithRetries } from "@oh-my-pi/pi-utils";
 
 // xdev mounting is default-on: discoverable tools like ast_edit unmount into
@@ -105,4 +106,30 @@ describe("read and write route xd:// device URLs", () => {
 		const rendered = writeToolRenderer.renderCall({ path: "xd://ast_edit", content }, options, uiTheme);
 		expect(rendered).toBeDefined();
 	});
+
+	it("docsAll inlines small device docs and falls back to a listing past the caps", async () => {
+		const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "write-xdev-docs-"));
+		try {
+			const session = xdevSession(tempDir);
+			await createTools(session);
+			const mounted = session.xdevRegistry?.list() ?? [];
+			expect(mounted.length).toBeGreaterThan(0);
+
+			// One device with a pathological description must fall back to the
+			// listing without starving the rest of the catalog.
+			const giant = Object.create(mounted[0]!) as (typeof mounted)[number];
+			Object.defineProperty(giant, "name", { value: "giant_mcp_tool" });
+			Object.defineProperty(giant, "description", { value: "x".repeat(XdevRegistry.DOCS_PER_DEVICE_CAP + 1) });
+			const registry = new XdevRegistry([...mounted, giant]);
+
+			const docs = registry.docsAll();
+			expect(docs.length).toBeLessThan(XdevRegistry.DOCS_TOTAL_BUDGET + XdevRegistry.DOCS_PER_DEVICE_CAP);
+			expect(docs).toContain(`## ${mounted[0]!.name}`);
+			expect(docs).toContain("## Additional devices (docs on demand)");
+			expect(docs).toContain("- xd://giant_mcp_tool —");
+			expect(docs).not.toContain("## giant_mcp_tool");
+		} finally {
+			await removeWithRetries(tempDir);
+		}
+	});
 });