FN-7035: split oversized test suites

Split oversized ChatView and notifier suites while updating the line-count baseline.

- Move ChatView core contract and interaction coverage into focused sibling test files.
- Move notifier runtime coverage into its own suite and share setup through a test harness.
- Document the line-count guard decision and ratchet baseline entries for existing growth.

Files changed:
 .../__tests__/ChatView.core-contracts.test.tsx     |  623 ++++++++
 .../__tests__/ChatView.core-interactions.test.tsx  | 1261 +++++++++++++++
 .../components/__tests__/ChatView.core.test.tsx    | 1652 +-------------------
 .../engine/src/__tests__/notifier.runtime.test.ts  |  810 ++++++++++
 .../engine/src/__tests__/notifier.test-harness.ts  |   71 +
 packages/engine/src/__tests__/notifier.test.ts     |  847 +---------
 scripts/check-file-line-count.mjs                  |    3 +
 scripts/line-count-baseline.json                   |   12 +-
 8 files changed, 2778 insertions(+), 2501 deletions(-)

Fusion-Task-Id: FN-7035
Fusion-Task-Lineage: 14cebb57-925b-41c7-9c8b-472f34b76fe2

scripts/check-file-line-count.mjs

@@ -25,6 +25,9 @@ FN-6917 re-confirms the `pnpm test`-blocking premise is stale because FN-5048 le
 
 FNXC:CI 2026-06-25-00:00:
 FN-7013 re-confirms the `pnpm test`-blocking premise is stale: FN-5048 removed this guard from pretest and left it opt-in under `check:line-count` only. Sixty-one current violations were re-ratcheted after organic feature/test growth and eight stale baseline entries were tightened or pruned. `AgentLogViewer.test.tsx` and `merger-ai.ts` were temporarily grandfathered after crossing the hard cap as long-existing files, with focused split follow-ups FN-7028 and FN-7029. Wholesale god-file shrink/refactor remains the long-term direction and stays deferred to dedicated follow-ups.
+
+FNXC:CI 2026-06-25-17:44:
+FN-7035 split the two new hard-cap crossers (`ChatView.core.test.tsx` and `notifier.test.ts`) into focused sibling suites rather than grandfathering them. Six existing grandfathered entries were re-ratcheted to current counts after organic test and feature growth; `store.ts` and `types.ts` drift was left out of scope for a follow-up. Wholesale god-file shrink remains long-term deferred work for dedicated refactors.
 */
 // Repo-wide guard: hand-written source files may not exceed a hard line-count
 // cap (MAX_LINES). This stops the next god-file from being born while leaving

scripts/line-count-baseline.json

@@ -7,19 +7,19 @@
   "packages/cli/src/commands/dashboard-tui/app.tsx": 4681,
   "packages/cli/src/commands/dashboard.ts": 3000,
   "packages/cli/src/extension.ts": 4704,
-  "packages/core/src/__tests__/agent-store.test.ts": 2997,
+  "packages/core/src/__tests__/agent-store.test.ts": 3003,
   "packages/core/src/__tests__/central-core.test.ts": 3263,
   "packages/core/src/__tests__/db.test.ts": 3606,
-  "packages/core/src/__tests__/mission-store.test.ts": 4519,
+  "packages/core/src/__tests__/mission-store.test.ts": 4525,
   "packages/core/src/__tests__/plugin-loader.test.ts": 2783,
   "packages/core/src/__tests__/store-settings.test.ts": 2249,
   "packages/core/src/agent-store.ts": 2946,
   "packages/core/src/central-core.ts": 3854,
-  "packages/core/src/db.ts": 5888,
+  "packages/core/src/db.ts": 5924,
   "packages/core/src/mission-store.ts": 4390,
   "packages/core/src/store.ts": 17358,
   "packages/core/src/types.ts": 7415,
-  "packages/dashboard/app/api/legacy.ts": 10821,
+  "packages/dashboard/app/api/legacy.ts": 10865,
   "packages/dashboard/app/components/AgentDetailView.tsx": 5400,
   "packages/dashboard/app/components/AgentsView.tsx": 2147,
   "packages/dashboard/app/components/ChatView.tsx": 4075,
@@ -28,7 +28,7 @@
   "packages/dashboard/app/components/MissionManager.tsx": 5042,
   "packages/dashboard/app/components/ModelOnboardingModal.tsx": 3212,
   "packages/dashboard/app/components/PlanningModeModal.tsx": 3531,
-  "packages/dashboard/app/components/QuickEntryBox.tsx": 2229,
+  "packages/dashboard/app/components/QuickEntryBox.tsx": 2288,
   "packages/dashboard/app/components/SettingsModal.tsx": 3505,
   "packages/dashboard/app/components/TaskCard.tsx": 2544,
   "packages/dashboard/app/components/TaskDetailModal.tsx": 4636,
@@ -42,7 +42,7 @@
   "packages/dashboard/app/components/__tests__/MailboxView.test.tsx": 2202,
   "packages/dashboard/app/components/__tests__/ModelOnboardingModal.test.tsx": 4679,
   "packages/dashboard/app/components/__tests__/PlanningModeModal.planning-flow.test.tsx": 3002,
-  "packages/dashboard/app/components/__tests__/QuickEntryBox.test.tsx": 4707,
+  "packages/dashboard/app/components/__tests__/QuickEntryBox.test.tsx": 4850,
   "packages/dashboard/app/components/__tests__/TaskCard.test.tsx": 5121,
   "packages/dashboard/app/components/__tests__/TaskChatTab.test.tsx": 2558,
   "packages/dashboard/app/components/__tests__/TaskDetailModal.inline-editing-and-integrations.test.tsx": 2917,