Enforce 100% per-file test coverage on packages/*/src

vitest coverage (v8 provider) with per-file 100% thresholds for
statements, branches, functions, and lines. Scope: our runtime source
only — types-only files, vendor/ (upstream code), and examples/
(exercised by the demo smoke test) are excluded. yarn test:coverage
runs the gate.

59 tests added to close every gap: llm generate-waterfall and adapter
disposal; assembler edge protocol (duplicate block-start, stragglers
after block-end, id fallback, usage omission, invariant violation);
the whole Inbox surface incl. the wakeup-overwrite race; LoopAgent
disposed-state throws and double-stop idempotence; config-driven agent
creation; loop backstop catches (throwing turn-start/turn-end
listeners, non-Error throws, non-JSON tool arguments); system-prompt
dynamic sections and disposer paths; tools errorMessage fallbacks and
the full schema-DSL emission matrix. Genuinely unreachable defensive
guards carry /* v8 ignore */ comments with stated reasons rather than
deletion (132 tests total).

vitest.config.ts

@@ -5,5 +5,24 @@ export default defineConfig({
   plugins: [tsconfigPaths({ projects: ['./tsconfig.test.json'] })],
   test: {
     include: ['packages/*/tests/**/*.spec.ts'],
+    coverage: {
+      provider: 'v8',
+      // Coverage measures OUR runtime source. Types-only files carry no
+      // executable code; vendor/ and examples/ are out of scope (examples are
+      // exercised by the demo smoke test instead).
+      include: ['packages/*/src/**/*.ts'],
+      exclude: ['packages/*/src/types.ts'],
+      // 100% or it doesn't merge (AGENTS.md: excessive tests are welcome).
+      // Per-file so a well-covered big file can't subsidize a bare one.
+      // Every v8 ignore comment must carry a reason — see AGENTS.md.
+      thresholds: {
+        perFile: true,
+        statements: 100,
+        branches: 100,
+        functions: 100,
+        lines: 100,
+      },
+      reporter: ['text', 'html'],
+    },
   },
 })