diff --git a/.agents/skills/test-t3-app/SKILL.md b/.agents/skills/test-t3-app/SKILL.md
index 6fde6fff30984..7ac0eb1106b32 100644
--- a/.agents/skills/test-t3-app/SKILL.md
+++ b/.agents/skills/test-t3-app/SKILL.md
@@ -5,10 +5,10 @@ description: Test T3 Code's web and desktop UI through its built-in Browser pane
 
 # Test T3 web and desktop
 
-Use T3's built-in Browser panel for verification. If its tools are absent or
-the panel reports unavailable, explain the blocker and stop verification.
-Do not install or switch to another automation system. For native mobile
-testing, use [test-t3-mobile](../test-t3-mobile/SKILL.md).
+Use T3's built-in Browser panel for verification. Follow the recovery steps
+below before declaring it unavailable. Do not install or switch to another
+automation system. For native mobile testing, use
+[test-t3-mobile](../test-t3-mobile/SKILL.md).
 
 ## Start the app
 
@@ -36,8 +36,13 @@ model, such as Haiku for Claude or Luna for Codex.
 
 ## Use the Browser panel
 
-Call `preview_status`, then `preview_open` if the Browser panel is
-closed. Navigate to the complete startup pairing URL once with
+Call `preview_status`. If no tab can be automated, call `preview_open`, including
+when status reports `available: false` or `tabId: null`. Status can report
+unavailable simply because no tab exists yet; opening a tab needs no user action.
+Stop verification and explain the blocker only if the tools are absent or
+`preview_open` reports unavailable or fails.
+
+Navigate to the complete startup pairing URL once with
 `preview_navigate`, then use `preview_snapshot` and T3's interaction tools.
 If the token was consumed or expired, run `node apps/server/src/bin.ts pair`
 for a fresh one. Keep using the same tab.
diff --git a/evals/mcp-tool-use/README.md b/evals/mcp-tool-use/README.md
index 3b817f574455f..fadea6438da46 100644
--- a/evals/mcp-tool-use/README.md
+++ b/evals/mcp-tool-use/README.md
@@ -26,6 +26,7 @@ Cases are JSON lines in `cases/`, one file per area. The case schema in `run.ts`
 - `kind`: `bad` reproduces a mistake, `guard` protects correct behavior, `control` is ordinary work.
 - `experience`: the real mistake, in a sentence. `source`: where it happened.
 - `setup`: the fake thread, its `world` (repo, branch, files, PRs, pages), `priorTurns`, and `mocks` for tool results.
+- `setup.priorTurns[].toolCalls[].resultFile`: load a repository-relative file as the tool result instead of copying its contents into the case. An empty `prompt` resumes a top-level thread after its last prior tool result without adding a user message. Side-chat and subagent setups require a nonempty prompt.
 - `expect`: the checks, such as `calls`, `callsMustNot`, `maxCalls`, `order`, `textMust`, and `linked`. Device cases also use `device` to check every child brief, forbid raw UI commands, bound failed device actions per user turn, and require artifact paths in completed final answers.
 
 Check that the case builds with `--dry-run --case <id>`. Then run it on the text before your fix, where it must fail, and on the text after, where it must pass.
diff --git a/evals/mcp-tool-use/cases/visual-preview.ndjson b/evals/mcp-tool-use/cases/visual-preview.ndjson
index 1940692d9fe17..1b9d713307e91 100644
--- a/evals/mcp-tool-use/cases/visual-preview.ndjson
+++ b/evals/mcp-tool-use/cases/visual-preview.ndjson
@@ -28,3 +28,5 @@
 {"id": "proactive-visual-ci-time-breakdown", "area": "visual-preview", "kind": "bad", "privacy": "commit-safe", "pattern": "data that reads better as a chart answered in prose only", "rule": "When a chart, diagram, or mockup says more than prose: html_preview, then html_render", "source": {"report": "agents used inline HTML visuals less often after #24850 made the rule ask-only"}, "experience": "The user shared CI job times over several runs and asked what eats the time. The agent answered in prose; a stacked chart would have shown it.", "setup": {"role": "top"}, "prompt": "CI got slow. Here are job times in minutes for the last 8 runs on main. What's eating the time?\n\nRun | install | typecheck | lint | test-server | test-web | build | e2e\n1 | 2.1 | 3.0 | 1.2 | 6.8 | 4.1 | 3.3 | 7.9\n2 | 2.0 | 3.1 | 1.1 | 6.9 | 4.0 | 3.4 | 8.2\n3 | 2.2 | 3.0 | 1.2 | 7.4 | 4.2 | 3.3 | 8.0\n4 | 2.1 | 3.2 | 1.3 | 9.8 | 4.1 | 3.5 | 8.1\n5 | 2.3 | 3.1 | 1.2 | 12.6 | 4.3 | 3.4 | 8.4\n6 | 2.2 | 3.3 | 1.2 | 13.1 | 4.2 | 3.6 | 12.9\n7 | 2.1 | 3.2 | 1.3 | 13.4 | 4.4 | 3.5 | 13.2\n8 | 2.2 | 3.2 | 1.2 | 13.0 | 4.3 | 3.4 | 13.5", "expect": {"calls": [{"tool": "html_render"}], "order": ["html_preview", "html_render"], "notCalls": ["preview_open", "preview_navigate"]}}
 {"id": "requested-after-video-for-edit", "area": "visual-preview", "kind": "bad", "privacy": "commit-safe", "pattern": "agent refuses requested browser recording of its own edit", "experience": "A user asked for an after video of a UI fix. The agent declined because the injected instructions prohibited preview for its own edits.", "rule": "Use preview when the user asks for browser work, including recording an edit.", "setup": {"role": "top", "context": "The UI fix is complete and a development server is already running at http://localhost:3000. Browser verification and recording are authorized.", "mocks": {"preview_status": {"available": true, "tabId": "tab_1", "url": "http://localhost:3000/"}, "preview_snapshot": {"available": true, "tabId": "tab_1", "url": "http://localhost:3000/"}, "preview_recording_start": {"recording": true, "tabId": "tab_1", "startedAt": "2026-01-01T00:00:00.000Z"}, "preview_recording_stop": {"id": "recording_1", "tabId": "tab_1", "path": "/tmp/after.webm", "mimeType": "video/webm", "sizeBytes": 1024, "createdAt": "2026-01-01T00:00:01.000Z"}}}, "prompt": "Use the T3 browser to verify the UI fix you just made and record an after video.", "expect": {"calls": [{"tool": "preview_recording_start"}, {"tool": "preview_recording_stop"}], "order": ["preview_recording_start", "preview_recording_stop"]}, "source": {"report": "A user requested an after video of a UI fix; the agent declined because preview was prohibited for its own edits."}}
 {"id": "dev-server-opened-blank-then-navigated", "area": "visual-preview", "kind": "bad", "pattern": "preview_open on a blank tab, then preview_navigate to the dev-server port", "experience": "Asked to open a dev server in the T3 preview, agents opened a blank tab and navigated it to the port in a second call. 121 of these pairs in a month of maintainer threads.", "rule": "preview_open takes a url but not a dev-server target", "privacy": "commit-safe", "setup": {"role": "top", "context": "CLAUDE.md says: for t3code browser work, use the server-side preview_* mcp tools, with `target: {kind: \"environment-port\", port: ...}` for dev servers in the current environment. The dev server for this repo is running; `vp run dev` printed `Local: http://localhost:5173/`.", "mocks": {"preview_status": {"available": true, "visible": false, "tabId": null, "url": null, "title": null, "loading": false, "profiles": [{"id": "default", "name": "Default"}], "defaultProfileId": "default"}, "preview_open": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5173/", "title": "Acme", "loading": false, "control": {"owner": "agent", "ownedByCaller": true}}, "preview_navigate": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5173/", "title": "Acme", "loading": false, "control": {"owner": "agent", "ownedByCaller": true}}}}, "prompt": "open the dev server in the t3 preview, i want to click around", "expect": {"calls": [{"tool": "preview_open", "args": {"target.port": 5173}}], "maxCalls": {"preview_open": 1, "preview_navigate": 0}}, "maxSteps": 6, "source": {"thread": "Maintainer threads, 2026-10: preview_open with no url followed by preview_navigate to an environment-port target, 121 times"}}
+{"id": "browser-status-reuses-existing-tab", "area": "visual-preview", "kind": "control", "privacy": "commit-safe", "pattern": "usable Browser tab needs no new tab", "experience": "An already paired, usable tab should be reused during verification.", "source": {"report": "Maintainer browser verification failure, 2026-11-03"}, "setup": {"role": "top", "context": "The UI fix is complete. The test server is healthy at http://localhost:5173 and its browser profile is already paired. The current tab can be automated.", "mocks": {"preview_status": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5173/", "tabs": [{"tabId": "tab_1", "url": "http://localhost:5173/", "owner": "agent", "ownedByCaller": true}], "control": {"owner": "agent", "ownedByCaller": true, "generation": 0}}, "preview_open": {"available": true, "visible": false, "tabId": "tab_1", "url": "http://localhost:5173/"}, "preview_snapshot": {"available": true, "tabId": "tab_1", "url": "http://localhost:5173/", "screenshotPath": "/tmp/after.png"}}, "priorTurns": [{"role": "user", "text": "Use the Browser panel to verify the UI fix and capture an after screenshot."}, {"role": "assistant", "toolCalls": [{"tool": "Bash", "input": {"command": "cat .agents/skills/test-t3-app/SKILL.md"}, "result": "", "resultFile": ".agents/skills/test-t3-app/SKILL.md"}]}, {"role": "assistant", "toolCalls": [{"tool": "preview_status", "input": {}, "result": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5173/", "tabs": [{"tabId": "tab_1", "url": "http://localhost:5173/", "owner": "agent", "ownedByCaller": true}], "control": {"owner": "agent", "ownedByCaller": true, "generation": 0}}}]}], "harness": "claude"}, "prompt": "", "expect": {"calls": [{"tool": "preview_snapshot"}], "callsMustNot": [{"tool": "preview_open", "args": {"reuseExistingTab": false}}]}, "maxSteps": 10, "notes": "Checks reuse of an existing usable tab. Screenshot saving is outside this control. Prior tool-result replay is validated on the Claude harness; Codex output wrapping needs separate validation."}
+{"id": "browser-resume-after-unavailable-status", "area": "visual-preview", "kind": "bad", "privacy": "commit-safe", "pattern": "closed Browser panel treated as unavailable automation", "experience": "The agent read test-t3-app, saw available false with no tab, and asked the user to open the panel instead of calling preview_open. Opening a tab succeeded on the next turn.", "source": {"report": "Maintainer browser verification failure, 2026-11-03; fresh skill read followed by unavailable status. Opus replay reproduces the stop on the old skill."}, "setup": {"role": "top", "context": "Repository instructions: Before web or desktop UI verification, read .agents/skills/test-t3-app/SKILL.md and follow it. If a skill causes you to stop or leave requested work unfinished, link the SKILL.md, quote the relevant instruction, and explain how it applies.", "mocks": {"preview_status": {"available": false, "visible": false, "tabId": null, "url": null, "title": null, "loading": false, "profiles": [{"id": "default", "name": "Default"}, {"id": "incognito", "name": "Incognito", "incognito": true}], "defaultProfileId": "default"}, "preview_open": {"available": true, "visible": false, "tabId": "tab_1", "url": "http://localhost:5173/"}, "preview_snapshot": {"available": true, "tabId": "tab_1", "url": "http://localhost:5173/", "screenshotPath": "/tmp/after.png"}}, "world": {"repo": "acme/app", "branch": "fix/permissions-popup", "status": "", "files": {"apps/web/src/components/ComposerContextPermissions.tsx": "export function ComposerContextPermissions() { return <PermissionsMenu side=\"top\" align=\"end\" />; }\n"}, "description": "The requested fix is already committed as a1b2c3d on fix/permissions-popup, ahead of main. It changes ComposerContextPermissions.tsx to open the permissions popup above its trigger. Dependencies are installed. No development server is running and no .t3 directory exists.", "commits": [{"sha": "a1b2c3d", "subject": "fix(web): open composer permissions above its button"}]}, "priorTurns": [{"role": "user", "text": "When I click Full access in the composer, open its permissions menu directly above that button."}, {"role": "assistant", "toolCalls": [{"tool": "Bash", "input": {"command": "git commit -am \"fix(web): open composer permissions above its button\""}, "result": "[fix/permissions-popup a1b2c3d] fix(web): open composer permissions above its button\n 1 file changed, 3 insertions(+), 1 deletion(-)"}]}, {"role": "assistant", "text": "Implemented. Clicking Full access opens the permissions menu above the button. Focused checks pass. Full-client visual verification remains undone."}, {"role": "user", "text": "before/after screenshot"}, {"role": "assistant", "toolCalls": [{"tool": "Bash", "input": {"command": "cat .agents/skills/test-t3-app/SKILL.md"}, "result": "", "resultFile": ".agents/skills/test-t3-app/SKILL.md"}]}, {"role": "assistant", "text": "I'll use the test-t3-app skill to capture the before and after states in the app."}, {"role": "assistant", "toolCalls": [{"tool": "preview_status", "input": {}, "result": {"available": false, "visible": false, "tabId": null, "url": null, "title": null, "loading": false, "profiles": [{"id": "default", "name": "Default"}, {"id": "incognito", "name": "Incognito", "incognito": true}], "defaultProfileId": "default"}}]}], "shellMocks": [{"match": "git status|ls .*\\.t3", "output": "ls: .t3: No such file or directory"}], "harness": "claude"}, "prompt": "", "expect": {"calls": [{"tool": "preview_open"}]}, "maxSteps": 8, "notes": "Resume at the failed decision after reading the skill and receiving available=false. Opus reproduces the premature stop; Sonnet did not reliably reproduce it. This checks recovery through preview_open, not completion of screenshots. Prior tool-result replay is validated on the Claude harness; Codex output wrapping needs separate validation."}
diff --git a/evals/mcp-tool-use/run.test.ts b/evals/mcp-tool-use/run.test.ts
index 217e505f5fcf5..6c24f18ac5063 100644
--- a/evals/mcp-tool-use/run.test.ts
+++ b/evals/mcp-tool-use/run.test.ts
@@ -394,6 +394,28 @@ it("replays earlier capability results with the model under test as the caller",
     .flatMap((message) => message.content)
     .find((block) => block.type === "tool_result" && String(block.content).includes("inherited"));
   assert.include(String(replayed?.content), '"inheritedModel":"claude-opus-5-5"');
+  const resumed = buildMessages(makeSample({ ...testCase, prompt: "" }, base));
+  assert.equal(resumed.at(-1)?.role, "user");
+  assert.equal(resumed.at(-1)?.content.at(-1)?.type, "tool_result");
+  for (const setup of [
+    {
+      ...testCase.setup,
+      sideChat: { parentThreadId: "thread-parent", digest: ["The permissions fix is committed."] },
+    },
+    { ...testCase.setup, role: "native-subagent" as const },
+    { ...testCase.setup, role: "delegated-child" as const },
+  ]) {
+    assert.throws(
+      () =>
+        buildMessages(
+          makeSample(
+            { ...testCase, prompt: "", setup },
+            { ...base, subagentContext: "Hook context" },
+          ),
+        ),
+      /Empty-prompt replay/,
+    );
+  }
 });
 
 it("gives each launched thread its own id, and reading it back shows that thread's brief", () => {
diff --git a/evals/mcp-tool-use/run.ts b/evals/mcp-tool-use/run.ts
index 3e6bb84f697be..02c5d8ce58e46 100644
--- a/evals/mcp-tool-use/run.ts
+++ b/evals/mcp-tool-use/run.ts
@@ -140,6 +140,8 @@ const PriorToolCall = Schema.Struct({
   input: Schema.Unknown,
   /** For a device tool, `"default"` runs the call on the world's devices for T3's result. */
   result: Schema.Unknown,
+  /** Repository-relative file whose current contents supply this tool result. */
+  resultFile: Schema.optional(Schema.String),
 });
 
 /**
@@ -275,6 +277,7 @@ export const McpToolUseCase = Schema.Struct({
       Schema.Struct({ parentThreadId: Schema.String, digest: Schema.Array(Schema.String) }),
     ),
   }),
+  /** Empty to resume a top-level thread without side-chat context after its last tool result. */
   prompt: Schema.String,
   /** Records for the context chips `prompt` links, projected as T3 sends them. */
   promptContext: Schema.optional(Schema.Struct({ records: Schema.Array(ComposerContextRecord) })),
@@ -880,6 +883,19 @@ export const buildMessages = (sample: Sample) => {
     else messages[messages.length - 1] = { role, content: [...last.content, ...blocks] };
   };
   const { role, context, delegateRole, priorTurns = [] } = testCase.setup;
+  const sideChat = testCase.setup.sideChat;
+  if (testCase.prompt === "" && (role !== "top" || sideChat !== undefined)) {
+    throw new Error(
+      `${testCase.id}: Empty-prompt replay requires a top-level thread without side-chat context.`,
+    );
+  }
+  const sideChatContext =
+    sideChat === undefined
+      ? undefined
+      : makeSideChatContext({
+          parentThreadId: ThreadId.make(sideChat.parentThreadId),
+          digest: sideChat.digest,
+        });
   const native = role === "native-subagent";
   const notes = [
     native
@@ -926,19 +942,11 @@ export const buildMessages = (sample: Sample) => {
     testCase.promptContext === undefined
       ? testCase.prompt
       : projectComposerContextForProvider({ text: testCase.prompt, ...testCase.promptContext });
-  const sideChat = testCase.setup.sideChat;
   const prompt =
-    sideChat === undefined
-      ? userText
-      : withInlineContext(
-          makeSideChatContext({
-            parentThreadId: ThreadId.make(sideChat.parentThreadId),
-            digest: sideChat.digest,
-          }),
-          userText,
-        );
+    sideChatContext === undefined ? userText : withInlineContext(sideChatContext, userText);
   const childPrompt = () => taskPrompt({ task: prompt, role: delegateRole });
-  push("user", text(role === "delegated-child" ? childPrompt() : prompt));
+  if (testCase.prompt !== "")
+    push("user", text(role === "delegated-child" ? childPrompt() : prompt));
   // Claude Code gives a subagent its SubagentStart hooks' context as a reminder after the task.
   if (native && base.subagentContext) {
     push("user", reminder(`SubagentStart hook additional context: ${base.subagentContext}`));
@@ -2125,12 +2133,35 @@ const main = Effect.gen(function* () {
   const wanted = flags.case?.flatMap((ids) => ids.split(","));
   const codex = isCodex(flags.model);
   const harness = codex ? "codex" : "claude";
-  const selected = cases.filter(
+  const selectedCases = cases.filter(
     ({ id, setup }) =>
       (wanted === undefined || wanted.includes(id)) &&
       (setup.harness === undefined || setup.harness === harness),
   );
-  if (selected.length === 0) return yield* Effect.die(new Error("No case matches --case."));
+  if (selectedCases.length === 0) return yield* Effect.die(new Error("No case matches --case."));
+  const selected = yield* Effect.forEach(selectedCases, (testCase) =>
+    Effect.gen(function* () {
+      const priorTurns = yield* Effect.forEach(testCase.setup.priorTurns ?? [], (turn) =>
+        Effect.gen(function* () {
+          const toolCalls = yield* Effect.forEach(turn.toolCalls ?? [], (call) =>
+            call.resultFile === undefined
+              ? Effect.succeed(call)
+              : fs
+                  .readFileString(path.resolve(import.meta.dirname, "../..", call.resultFile))
+                  .pipe(Effect.map((result) => ({ ...call, result }))),
+          );
+          return { ...turn, toolCalls };
+        }),
+      );
+      return {
+        ...testCase,
+        setup: {
+          ...testCase.setup,
+          priorTurns,
+        },
+      };
+    }),
+  );
   // Trimmed captures without user data ship beside the cases. `--template` also takes a raw
   // CLIProxyAPI capture.
   const templatePath =