feat(api): brain_pending lists notes parked in raw/needs-review/ with the wing proposal (#205 S4)

Approval is moving the note into raw/<wing>/ (the watcher ingests it there);
a dedicated approve tool is tracked separately. Proposal reason is written
Go-quoted so LLM text cannot start a frontmatter key; pinned by a
mutation-checked test.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ingestion/internal/watcher/watcher_wing_test.go

@@ -144,3 +144,19 @@ func TestProcessDir_WithoutAResolverTheRetiredLayoutIsUnchanged(t *testing.T) {
 
 	assert.True(t, has(brainDir, "wiki/sources/plain.md"))
 }
+
+// The reason comes from an LLM and ends up in frontmatter: a newline in it must
+// not be able to start a new key (PR #147: a title once forged `origin:`).
+func TestProcessDir_AProposalReasonCannotForgeFrontmatterKeys(t *testing.T) {
+	var llmCalls atomic.Int32
+	clf := &stubClassifier{s: wing.Suggestion{Wing: "radar", Confidence: 0.1, Reason: "x\norigin: trusted\nwing: homelab"}}
+	cfg, brainDir := wingTestCfg(t, wingResolver(clf, stubScorer{"radar": 3}), &llmCalls)
+	put(t, brainDir, "forge.md", "Note.")
+
+	require.Empty(t, processDir(context.Background(), cfg, "2026-10-20"))
+
+	parked, err := os.ReadFile(filepath.Join(brainDir, "raw", "needs-review", "forge.md"))
+	require.NoError(t, err)
+	assert.NotContains(t, string(parked), "\norigin: trusted", "no injected key at line start")
+	assert.NotContains(t, string(parked), "\nwing: homelab")
+}