feat(web): real linked Signal projection from signalIssueAttachments

Replace the deliberate signalCount of 0 with authenticated linked-Signal
data from the Lane A signalIssueAttachments relation.

- Add listLinkedSignalsForProject query (user-authenticated via
  requireProjectMember) returning issue-grouped LinkedSignalView data
  using the existing by_issue index. One query serves both card counts
  and expanded detail.
- Update work-unit-projection builders to accept linkedSignals param;
  LinkedSignal type with signalId, title, summary, sourceCount, createdAt.
- Feed real attachment data into collapsed card signalCount and expanded
  detail linked-signal list with provenance (source count, relative time).
- Add signal.attached event handler to activity timeline projection.
- 32 tests including 4 linked-signal projection tests, 1 signal.attached
  activity mapping test, and cross-issue signal isolation test proving
  issue A cannot inherit issue B's linked signals.

apps/web/src/hooks/work-os/use-work-os.ts

@@ -14,6 +14,7 @@ import {
   eventsForIssue,
 } from "@/lib/work-os/work-unit-projection";
 import type {
+  LinkedSignal,
   WorkUnitCard,
   WorkUnitDetail,
 } from "@/lib/work-os/work-unit-projection";
@@ -28,7 +29,6 @@ export interface SignalItem {
 export type ComposerMode = "project" | "work-unit";
 
 export interface WorkOsState {
-  // Project
   readonly projects: ReturnType<typeof useProjectWorkspace>["projects"];
   readonly selectedProject: ReturnType<
     typeof useProjectWorkspace
@@ -40,7 +40,6 @@ export interface WorkOsState {
   readonly setRepository: (value: string) => void;
   readonly connectRepository: () => Promise<void>;
 
-  // Work units
   readonly workUnitCards: readonly WorkUnitCard[];
   readonly selectedIssue: ReturnType<
     typeof useProjectWorkspace
@@ -55,20 +54,36 @@ export interface WorkOsState {
   readonly issueBody: string;
   readonly setIssueBody: (value: string) => void;
 
-  // Signals (project-scoped, displayed globally — not attributed to any issue)
   readonly signals: readonly SignalItem[];
 
-  // Chat
   readonly composerMode: ComposerMode;
   readonly setComposerMode: (mode: ComposerMode) => void;
   readonly projectAgent: ChatAgentState;
   readonly workUnitAgent: ChatAgentState;
 
-  // Meta
   readonly pendingAction: string | null;
   readonly error: string | null;
 }
 
+const toLinkedSignals = (
+  entries:
+    | readonly {
+        readonly signalId: Id<"signals">;
+        readonly title: string;
+        readonly summary: string;
+        readonly sourceCount: number;
+        readonly createdAt: number;
+      }[]
+    | undefined
+): readonly LinkedSignal[] =>
+  (entries ?? []).map((entry) => ({
+    createdAt: entry.createdAt,
+    signalId: entry.signalId,
+    sourceCount: entry.sourceCount,
+    summary: entry.summary,
+    title: entry.title,
+  }));
+
 export const useWorkOs = (): WorkOsState => {
   const workspace = useProjectWorkspace();
   const orgState = usePersonalOrganization();
@@ -76,8 +91,6 @@ export const useWorkOs = (): WorkOsState => {
 
   const activeProjectId = workspace.selectedProjectId;
 
-  // Work-unit-scoped project-manager agent. Stays dormant until an issue is
-  // selected, then follows that issue identity across re-renders.
   const workUnitFlue = useFlueAgent({
     id: workspace.selectedIssueId
       ? String(workspace.selectedIssueId)
@@ -93,9 +106,7 @@ export const useWorkOs = (): WorkOsState => {
     status: workspace.selectedIssueId ? workUnitFlue.status : "idle",
   };
 
-  // Signals scoped to the active project. These are displayed as project-level
-  // evidence, not attributed to any specific work unit (no signal-to-issue
-  // relation exists yet).
+  // Project-level signals for the global sidebar panel.
   const allSignals = useQuery(
     api.signals.list,
     orgState.organizationId
@@ -116,7 +127,13 @@ export const useWorkOs = (): WorkOsState => {
       }));
   }, [allSignals, activeProjectId]);
 
-  // Composer mode tracks the selection by default but can be overridden.
+  // All linked signals for the active project, grouped by issue id.
+  // Used for card counts and detail display.
+  const linkedByIssue = useQuery(
+    api.signals.listLinkedSignalsForProject,
+    activeProjectId ? { projectId: activeProjectId } : "skip"
+  );
+
   const [composerMode, setComposerMode] = useState<ComposerMode>("project");
 
   const selectIssue = (issueId: Id<"projectIssues"> | null) => {
@@ -124,18 +141,21 @@ export const useWorkOs = (): WorkOsState => {
     setComposerMode(issueId ? "work-unit" : "project");
   };
 
-  // Work unit card projections — derived from per-issue events only.
   const workUnitCards = useMemo<readonly WorkUnitCard[]>(() => {
     if (!workspace.issues) {
       return [];
     }
     return workspace.issues.map((issue) => {
       const issueEvents = eventsForIssue(workspace.events, issue._id);
-      return buildWorkUnitCard({ issue, issueEvents });
+      const linked = toLinkedSignals(linkedByIssue?.[String(issue._id)]);
+      return buildWorkUnitCard({
+        issue,
+        issueEvents,
+        linkedSignals: linked,
+      });
     });
-  }, [workspace.issues, workspace.events]);
+  }, [workspace.issues, workspace.events, linkedByIssue]);
 
-  // Selected work unit detail — same per-issue derivation.
   const selectedDetail = useMemo<WorkUnitDetail | null>(() => {
     if (!workspace.selectedIssue) {
       return null;
@@ -144,11 +164,15 @@ export const useWorkOs = (): WorkOsState => {
       workspace.events,
       workspace.selectedIssue._id
     );
+    const linked = toLinkedSignals(
+      linkedByIssue?.[String(workspace.selectedIssue._id)]
+    );
     return buildWorkUnitDetail({
       issue: workspace.selectedIssue,
       issueEvents,
+      linkedSignals: linked,
     });
-  }, [workspace.selectedIssue, workspace.events]);
+  }, [workspace.selectedIssue, workspace.events, linkedByIssue]);
 
   return {
     composerMode,