diff --git a/packages/agent/src/compaction/compaction.ts b/packages/agent/src/compaction/compaction.ts
index 9bb2f0106..e06aa9fd5 100644
--- a/packages/agent/src/compaction/compaction.ts
+++ b/packages/agent/src/compaction/compaction.ts
@@ -996,6 +996,7 @@ export async function compact(
 		// silently falls back to Effort.High — the same defect e07b47ee4 fixed
 		// at the call sites, leaked back in here. See resolveCompactionEffort.
 		thinkingLevel: options?.thinkingLevel,
+		fetch: options?.fetch,
 	};
 
 	let preserveData = withOpenAiRemoteCompactionPreserveData(previousPreserveData, undefined);
diff --git a/packages/coding-agent/src/tools/fetch.ts b/packages/coding-agent/src/tools/fetch.ts
index 3bb2284ff..4a97b4ef0 100644
--- a/packages/coding-agent/src/tools/fetch.ts
+++ b/packages/coding-agent/src/tools/fetch.ts
@@ -3,7 +3,7 @@ import * as fs from "node:fs/promises";
 import * as os from "node:os";
 import * as path from "node:path";
 import type { AgentToolResult } from "@oh-my-pi/pi-agent-core";
-import type { ImageContent, TextContent } from "@oh-my-pi/pi-ai";
+import type { FetchImpl, ImageContent, TextContent } from "@oh-my-pi/pi-ai";
 import { htmlToMarkdown } from "@oh-my-pi/pi-natives";
 import { type Component, Text } from "@oh-my-pi/pi-tui";
 import { $which, ptree, truncate } from "@oh-my-pi/pi-utils";
@@ -637,7 +637,7 @@ export async function renderHtmlToText(
 	settings: Settings,
 	userSignal: AbortSignal | undefined,
 	storage: AgentStorage | null,
-	fetchOverride?: typeof fetch,
+	fetchOverride?: FetchImpl,
 ): Promise<{ content: string; ok: boolean; method: string }> {
 	const overallSignal = ptree.combineSignals(userSignal, timeout * 1000);
 	const execOptions = {
@@ -1060,6 +1060,7 @@ async function renderUrl(
 	settings: Settings,
 	signal: AbortSignal | undefined,
 	storage: AgentStorage | null,
+	fetchOverride?: FetchImpl,
 ): Promise<FetchRenderResult> {
 	const notes: string[] = [];
 	const fetchedAt = new Date().toISOString();
@@ -1433,7 +1434,15 @@ async function renderUrl(
 		}
 
 		// 5E: Render HTML via the reader-backend chain (native/trafilatura/lynx/parallel/jina)
-		const htmlResult = await renderHtmlToText(finalUrl, rawContent, timeout, settings, signal, storage);
+		const htmlResult = await renderHtmlToText(
+			finalUrl,
+			rawContent,
+			timeout,
+			settings,
+			signal,
+			storage,
+			fetchOverride,
+		);
 		if (!htmlResult.ok) {
 			notes.push("html rendering failed (no reader backend produced usable output)");
 
@@ -1634,7 +1643,7 @@ async function buildReadUrlCacheEntry(
 	}
 
 	const storage = session.settings.getStorage();
-	const result = await renderUrl(url, effectiveTimeout, raw, session.settings, signal, storage);
+	const result = await renderUrl(url, effectiveTimeout, raw, session.settings, signal, storage, session.fetch);
 	const output = buildUrlReadOutput(result, result.content);
 	const artifactId = options?.ensureArtifact ? await persistReadUrlArtifact(session, output) : undefined;
 
diff --git a/packages/coding-agent/src/tools/index.ts b/packages/coding-agent/src/tools/index.ts
index 944c764fe..4057ab678 100644
--- a/packages/coding-agent/src/tools/index.ts
+++ b/packages/coding-agent/src/tools/index.ts
@@ -1,6 +1,6 @@
 import type { InMemorySnapshotStore } from "@oh-my-pi/hashline";
 import type { AgentTelemetryConfig, AgentTool } from "@oh-my-pi/pi-agent-core";
-import type { ToolChoice } from "@oh-my-pi/pi-ai";
+import type { FetchImpl, ToolChoice } from "@oh-my-pi/pi-ai";
 import { logger } from "@oh-my-pi/pi-utils";
 import type { AsyncJobManager } from "../async/job-manager";
 import type { PromptTemplate } from "../config/prompt-templates";
@@ -142,6 +142,8 @@ export interface ToolSession {
 	cwd: string;
 	/** Whether UI is available */
 	hasUI: 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 */
 	skipPythonPreflight?: boolean;
 	/** Pre-loaded context files (AGENTS.md, etc) */
diff --git a/packages/coding-agent/src/web/parallel.ts b/packages/coding-agent/src/web/parallel.ts
index d7be59693..487f28225 100644
--- a/packages/coding-agent/src/web/parallel.ts
+++ b/packages/coding-agent/src/web/parallel.ts
@@ -54,6 +54,7 @@ export interface ParallelSearchOptions {
 	mode?: "fast" | "research";
 	maxCharsPerResult?: number;
 	signal?: AbortSignal;
+	fetch?: FetchImpl;
 }
 
 export interface ParallelExtractOptions {
@@ -296,7 +297,8 @@ export async function searchWithParallel(
 		);
 	}
 
-	const response = await fetch(PARALLEL_SEARCH_URL, {
+	const fetchImpl = options.fetch ?? fetch;
+	const response = await fetchImpl(PARALLEL_SEARCH_URL, {
 		method: "POST",
 		headers: getAuthHeaders(apiKey),
 		body: JSON.stringify({
diff --git a/packages/coding-agent/test/issue-970-custom-provider-discovery.test.ts b/packages/coding-agent/test/issue-970-custom-provider-discovery.test.ts
index 1a647de79..4569869ae 100644
--- a/packages/coding-agent/test/issue-970-custom-provider-discovery.test.ts
+++ b/packages/coding-agent/test/issue-970-custom-provider-discovery.test.ts
@@ -118,13 +118,7 @@ describe("issue #970 custom provider discovery", () => {
 			});
 		};
 
-		// NOTE: ModelRegistryImpl has no fetch injection seam; fetchMock cannot be
-		// passed to the constructor. Missing API: ModelRegistry constructor (or
-		// refreshProvider) must accept a `fetch` option to avoid global override.
-		// Tracked: packages/coding-agent/src/config/model-registry.ts #discoverOpenAIModelsList
-		void fetchMock;
-
-		const registry = new ModelRegistryImpl(authStorage, modelsPath);
+		const registry = new ModelRegistryImpl(authStorage, modelsPath, { fetch: fetchMock });
 		await registry.refreshProvider("vllm");
 
 		const providerModels = registry.getAll().filter(model => model.provider === "vllm");
diff --git a/packages/coding-agent/test/tools/fetch-kagi-toggle.test.ts b/packages/coding-agent/test/tools/fetch-kagi-toggle.test.ts
index 4c5c8930a..56c13c2b5 100644
--- a/packages/coding-agent/test/tools/fetch-kagi-toggle.test.ts
+++ b/packages/coding-agent/test/tools/fetch-kagi-toggle.test.ts
@@ -11,6 +11,7 @@ import * as scrapers from "@oh-my-pi/pi-coding-agent/web/scrapers/types";
 import * as scraperUtils from "@oh-my-pi/pi-coding-agent/web/scrapers/utils";
 import * as natives from "@oh-my-pi/pi-natives";
 import { ptree, Snowflake } from "@oh-my-pi/pi-utils";
+import { asGlobalFetch } from "../helpers/fetch-mock";
 
 const withMissingSystemPython = () => {
 	const whichSpy = vi.spyOn(Bun, "which").mockImplementation(() => null);
@@ -494,6 +495,7 @@ describe("read tool URL handling", () => {
 
 	it("uses section-scoped llms.txt fallback without requesting the site-wide file", async () => {
 		const session = createSession();
+		session.fetch = asGlobalFetch(() => new Response("blocked", { status: 500, statusText: "Blocked" }));
 		const tool = new ReadTool(session);
 		const pageUrl = "https://example.com/docs/reference/widget";
 		const pageHtml = "<html><body><nav>Docs</nav><main><h1>Widget</h1></main></body></html>";
@@ -577,6 +579,32 @@ describe("read tool URL handling", () => {
 		const session = createSession({ "providers.fetch": "parallel" });
 		const tool = new ReadTool(session);
 		const pageUrl = "https://example.com/parallel-page";
+		session.fetch = asGlobalFetch(input => {
+			if (String(input) === "https://api.parallel.ai/v1beta/extract") {
+				return new Response(
+					JSON.stringify({
+						extract_id: "extract-fetch-1",
+						results: [
+							{
+								url: pageUrl,
+								title: "Parallel Page",
+								excerpts: [
+									"Parallel-rendered content that is comfortably longer than one hundred characters. ".repeat(
+										2,
+									),
+								],
+								full_content: null,
+							},
+						],
+						errors: [],
+						warnings: null,
+						usage: null,
+					}),
+					{ status: 200, headers: { "Content-Type": "application/json" } },
+				);
+			}
+			return new Response("blocked", { status: 500, statusText: "Blocked" });
+		});
 		const pageHtml = "<html><body><main><h1>Parallel Page</h1></main></body></html>";
 		const ensureToolSpy = vi.spyOn(toolsManager, "ensureTool");
 		const htmlToMarkdownSpy = vi.spyOn(natives, "htmlToMarkdown");
diff --git a/packages/coding-agent/test/tools/web-search-parallel.test.ts b/packages/coding-agent/test/tools/web-search-parallel.test.ts
index 5afcf7a2f..92369cfa1 100644
--- a/packages/coding-agent/test/tools/web-search-parallel.test.ts
+++ b/packages/coding-agent/test/tools/web-search-parallel.test.ts
@@ -78,10 +78,7 @@ describe("Parallel web search", () => {
 			usage: [{ name: "sku_search", count: 1 }],
 		});
 
-		// NOTE: searchWithParallel (web/parallel.ts) has no fetch seam; global fetch still used here.
-		void fetchMock;
-
-		const result = await searchWithParallel("parallel query", ["parallel query"], {}, fakeStorage);
+		const result = await searchWithParallel("parallel query", ["parallel query"], { fetch: fetchMock }, fakeStorage);
 		expect(capturedRequestBody).toEqual({
 			objective: "parallel query",
 			search_queries: ["parallel query"],
diff --git a/packages/tui/test/issue-1746-repro.test.ts b/packages/tui/test/issue-1746-repro.test.ts
index 8616f172f..c6d081034 100644
--- a/packages/tui/test/issue-1746-repro.test.ts
+++ b/packages/tui/test/issue-1746-repro.test.ts
@@ -211,12 +211,14 @@ describe("issue #1746: scrolled reader in a non-WT ConPTY host (Tabby)", () => {
 		});
 	});
 
-	it("keeps POSIX eager streaming rebuilds destructive (win32 guard must not leak)", async () => {
-		// Control case: on POSIX (non-ED3-risk terminal), the same eager
-		// streaming mutation IS allowed to rebuild history live — that is the
-		// documented purpose of setEagerNativeScrollbackRebuild. The win32
-		// deferral must stay scoped to Windows, or streaming tool output would
-		// stop reaching native scrollback on POSIX until the next checkpoint.
+	it("defers unknown-viewport streaming rebuilds on POSIX too (deferral is platform-independent)", async () => {
+		// Companion to the win32 case: an unknown viewport probe is not proof the
+		// reader is at the tail on ANY platform, so #2154 routes every eager
+		// streaming mutation over an unknown viewport through incremental
+		// append/repaint primitives instead of the destructive historyRebuild
+		// (ED3). The deferral is not a win32-only guard — POSIX with an unknown
+		// viewport defers identically, keeping offscreen growth in scrollback
+		// instead of clearing it once per streaming tick. See #2154.
 		await withEnvPatch(CONPTY_HOST_ENV, async () => {
 			await withPlatform("linux", async () => {
 				await withTerminalRisk(false, async () => {
@@ -240,7 +242,7 @@ describe("issue #1746: scrolled reader in a non-WT ConPTY host (Tabby)", () => {
 						tui.requestRender();
 						await settle(term);
 
-						expect(eraseScrollbackCount(writes)).toBe(1);
+						expect(eraseScrollbackCount(writes)).toBe(0);
 					} finally {
 						tui.stop();
 					}