perf: main-process reconcile cache — stop refetching the repo on every tool call

A full reconcile is ~2N gitea calls (deps + timelines per issue). Every agent
tool call (query_project) was doing a fresh one; the UI reconcile and the agent
didn't share anything. Now a single in-memory snapshot cache backs both.

- gitea.ts: getSnapshot(client, { maxAgeMs }) — reads within the window reuse the
  cache; maxAgeMs:0 forces fresh. invalidateSnapshot() drops it. The explicit UI
  reconcile forces fresh (and warms the cache); agent tool calls tolerate a 30s
  TTL to stay responsive; applyChange + createIssues invalidate so the board and
  forecast reflect the write immediately.
- model.ts: query_project reads getSnapshot (30s TTL) instead of reconciling live.

This is the SQLite mirror's cache semantics in memory — rebuildable, the durable
truth stays in gitea (purity split, D4). Persistent SQLite (offline + instant
boot) is a separate slice: Electron 34's Node 20 has no node:sqlite, so it needs
better-sqlite3 + electron-rebuild or sql.js/WASM — deferred as its own decision.

Verified: desktop typecheck clean, 14 fixture e2e green, live Reginald still
answers correctly from the cache (writes invalidate → board stays correct).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/desktop/src/main/model.ts

@@ -26,7 +26,13 @@ import {
 } from '@commitea/core'
 import { ipcMain } from 'electron'
 
-import { appendDirectiveEntry, getGiteaClient, getPmStateClient, reconcileSnapshot } from './gitea.js'
+import {
+  AGENT_SNAPSHOT_TTL_MS,
+  appendDirectiveEntry,
+  getGiteaClient,
+  getPmStateClient,
+  getSnapshot,
+} from './gitea.js'
 
 /** Small local model for prose + the read tool; big model reserved for later decomposition. */
 function resolveModelRouter(): ModelRouter | null {
@@ -93,7 +99,8 @@ export function registerModelIpc(): void {
     const execute = async (name: string, args: unknown) => {
       if (!client) return { error: 'gitea is not configured' }
       if (name === 'query_project') {
-        const snap = await reconcileSnapshot(client)
+        // reuse a recent reconcile — a multi-tool turn shouldn't refetch the repo each call
+        const snap = await getSnapshot(client, { maxAgeMs: AGENT_SNAPSHOT_TTL_MS })
         const a = (args ?? {}) as { view: ProjectView; filters?: QueryFilters }
         return buildProjectView(a.view, a.filters, snap, new Date())
       }