FN-6103: align chat stop button sizing with composer height

Align the regular chat stop button with the composer control sizing while quarantining an unrelated flaky room test.

- define a shared chat input control size variable and apply it to send/stop buttons for consistent width and minimum height
- update the chat input autosize CSS test to assert the shared control size contract and textarea minimum height
- quarantine the unrelated flaky ChatView rooms test in the dashboard Vitest config and quarantine ledger per policy

Files changed:
 packages/dashboard/app/components/ChatView.css       | 20 +++++++++++++-------
 .../__tests__/ChatView.chat-input-autosize.test.tsx  | 16 +++++++++++-----
 packages/dashboard/vitest.config.ts                  |  3 ++-
 scripts/lib/test-quarantine.json                     |  8 +++++++-
 4 files changed, 33 insertions(+), 14 deletions(-)

Fusion-Task-Id: FN-6103

Fusion-Task-Lineage: 3efc95ba-9369-4022-aa6e-f1981485caea

packages/dashboard/app/components/ChatView.css

@@ -1372,6 +1372,8 @@
 }
 
 .chat-input-row {
+  --chat-input-control-size: calc(var(--space-lg) * 2.5);
+
   display: flex;
   align-items: flex-end;
   gap: var(--space-sm);
@@ -1480,8 +1482,8 @@
 }
 
 .chat-input-send {
-  width: 36px;
-  height: 36px;
+  width: var(--chat-input-control-size);
+  min-height: var(--chat-input-control-size);
   border-radius: 50%;
   border: none;
   background: var(--accent);
@@ -1499,8 +1501,8 @@
 }
 
 .chat-input-stop {
-  width: 36px;
-  height: 36px;
+  width: var(--chat-input-control-size);
+  min-height: var(--chat-input-control-size);
   border-radius: var(--radius-md);
   border: none;
   background: color-mix(in srgb, var(--color-error) 15%, transparent);
@@ -1869,13 +1871,17 @@
   }
 
   /* primary touch targets per AGENTS.md convention */
-  .chat-attach-btn,
-  .chat-input-send,
-  .chat-input-stop {
+  .chat-attach-btn {
     min-width: calc(var(--space-lg) * 2.25);
     min-height: calc(var(--space-lg) * 2.25);
   }
 
+  .chat-input-send,
+  .chat-input-stop {
+    min-width: var(--chat-input-control-size);
+    min-height: var(--chat-input-control-size);
+  }
+
   .chat-attachment-preview {
     width: calc(var(--space-xl) * 2.5);
     height: calc(var(--space-xl) * 2.5);

packages/dashboard/app/components/__tests__/ChatView.chat-input-autosize.test.tsx

@@ -15,16 +15,22 @@ describe("ChatView chat input autosize", () => {
     expect(textareaRule?.[0]).toContain("overflow-y: hidden");
   });
 
-  it("keeps the stop button dimensions aligned with the send button", () => {
+  it("keeps the stop button dimensions aligned with the send button and textarea minimum", () => {
+    const rowRule = chatViewCss.match(/\.chat-input-row\s*\{[^}]*\}/);
+    const textareaRule = chatViewCss.match(/\.chat-input-textarea\s*\{[^}]*\}/);
     const sendRule = chatViewCss.match(/\.chat-input-send\s*\{[^}]*\}/);
     const stopRule = chatViewCss.match(/\.chat-input-stop\s*\{[^}]*\}/);
 
+    expect(rowRule).not.toBeNull();
+    expect(textareaRule).not.toBeNull();
     expect(sendRule).not.toBeNull();
     expect(stopRule).not.toBeNull();
-    expect(sendRule?.[0]).toContain("width: 36px");
-    expect(sendRule?.[0]).toContain("height: 36px");
-    expect(stopRule?.[0]).toContain("width: 36px");
-    expect(stopRule?.[0]).toContain("height: 36px");
+    expect(rowRule?.[0]).toContain("--chat-input-control-size: calc(var(--space-lg) * 2.5)");
+    expect(textareaRule?.[0]).toContain("min-height: 40px");
+    expect(sendRule?.[0]).toContain("width: var(--chat-input-control-size)");
+    expect(sendRule?.[0]).toContain("min-height: var(--chat-input-control-size)");
+    expect(stopRule?.[0]).toContain("width: var(--chat-input-control-size)");
+    expect(stopRule?.[0]).toContain("min-height: var(--chat-input-control-size)");
   });
 
   it("clamps oversized textarea growth to the new max height", () => {

packages/dashboard/vitest.config.ts

@@ -231,7 +231,7 @@ const qualityAppComponentBatchBTests = buildComponentQualityInclude(batchedQuali
 const qualityAppAppOnlyTests = ["app/components/__tests__/App.test.tsx"];
 const qualityAppChatOnlyTests = ["app/components/__tests__/ChatView.test.tsx"];
 const qualityAppSettingsOnlyTests = ["app/components/__tests__/SettingsModal.test.tsx"];
-
+const quarantinedDashboardTests = ["app/components/__tests__/ChatView.rooms.test.tsx"];
 
 const qualityApiTests = [
   // Critical HTTP/server behavior: auth, task/project/settings mutation,
@@ -318,6 +318,7 @@ export default defineConfig({
     minWorkers: 1,
     fileParallelism: true,
     isolate: true,
+    exclude: quarantinedDashboardTests,
     // Dashboard route and integration-heavy suites can exceed the Vitest
     // 5s default under workspace-concurrent runs.
     testTimeout: 15_000,

scripts/lib/test-quarantine.json

@@ -1,4 +1,10 @@
 {
   "$comment": "Flaky-test quarantine ledger (deletion ratchet — see AGENTS.md 'Flaky tests: quarantine on sight' and docs/testing.md 'Quarantine ledger and the deletion ratchet'). A test observed failing without a corresponding real bug is quarantined ON SIGHT: add an entry here AND a matching one-line `exclude` entry in that package's vitest config, in the same commit. Every entry needs a non-empty `reason` (link the failing run) and a `quarantinedAt` date — the entry expires 14 days later, at which point the test file is DELETED unless someone rescues it with evidence it catches real regressions plus a root-cause fix (never appeasement). There is deliberately no loader module and no automation around this file: it is a dated record, the vitest config exclude is the mechanism, and the sweep is policy executed by whoever touches the suite.",
-  "entries": []
+  "entries": [
+    {
+      "file": "packages/dashboard/app/components/__tests__/ChatView.rooms.test.tsx",
+      "reason": "FN-6103 workspace pnpm test observed flaky mobile visibility restore assertion: expected scrollTop 1180, received 300 in ChatView.rooms.test.tsx:805; unrelated to CSS-only composer button sizing change.",
+      "quarantinedAt": "2026-06-09"
+    }
+  ]
 }