docs(adr): record Bun 1.4.3 verification results and decisions

Stable Bun 1.4.3 runs installs, the development server, standalone type
checks, the native test runner and a Bun.serve static server. Native
lint/fmt are canary-only, and Angular's server build needs Node loader
hooks Bun does not apply, so the spec now keeps ESLint/Prettier until a
stable release, builds Angular client-only behind a Bun static server,
converts line coverage from lcov, and replaces the heap cap with a
container memory limit.

Refs #289

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

docs/bun-adoption.md

@@ -1,7 +1,8 @@
 # Bun Runtime and Native Tooling — Development Spec
 
-Status: local draft synthesized from the agreed individual decisions. Integration
-feasibility remains unverified; ADR 0009 remains proposed.
+Status: the agreed decisions are amended by the verification results in #289,
+recorded below. ADR 0009 remains proposed until the migration passes its final
+gate.
 
 ## Problem Statement
 
@@ -104,6 +105,75 @@ The following acceptance criteria define completion:
   native-tool documentation. Select the exact version only after verifying the
   required capabilities together.
 
+## Verification Results and Decisions (#289)
+
+Probes ran on 2026-10-17 against the stable Bun `1.4.3` release (`1.4.3+c6da4a4d3`)
+from a clean checkout. "Node unavailable" means a `PATH` holding only a `bun`
+executable plus `/usr/bin:/bin`, with `command -v node` failing.
+
+**Verified:**
+
+- **Install.** `bun install --frozen-lockfile` succeeds and leaves `bun.lock`
+  unchanged.
+- **Runtime.** Package binaries with a `#!/usr/bin/env node` shebang (`ng`,
+  `eslint`, `prettier`, `tsc`) run on Bun only with `--bun`. Without it they use
+  Node when Node is on `PATH`, so every such command must pass `--bun`
+  explicitly. Spawned build children are native executables (esbuild,
+  dart-sass); Angular's workers are threads of the Bun process.
+- **Development server.** `bun --bun x ng serve` serves the application and
+  direct navigation to `/benchmark` with Node unavailable.
+- **Type checking.** `bun check -p tsconfig.app.json` and
+  `-p tsconfig.spec.json` match `tsc` 6 on the clean tree and catch injected
+  application and test type errors. Only the Angular build catches template
+  errors, as expected.
+- **Tests.** `bun test` runs the whole functional suite with a preload that
+  compiles components through Angular's JIT transform with inlined templates,
+  sets up jsdom, TestBed and zoneless change detection, plus a small shim for
+  the Vitest APIs Bun lacks (`stubGlobal`, `unstubAllGlobals`, `waitFor`,
+  `advanceTimersByTimeAsync`, `expect.poll`, `toHaveBeenCalledExactlyOnceWith`,
+  `setSystemTime` ordering and Date-only fake timers). Real-worker specs work
+  with Node unavailable. `--isolate` or `--parallel` is required for per-file
+  isolation. No spec uses snapshots.
+- **Server.** `Bun.serve` passes route, asset, cache-header, missing-file and
+  path-traversal checks.
+- **CI scripts.** The policy regression script passes under Bun. The image
+  regression script needs its fake `docker` shebang changed from `node` to
+  `bun`.
+
+**Decisions taken after the probes:**
+
+- **Linter and formatter.** Native `bun lint` and `bun fmt` exist only in canary
+  builds (`1.4.4-canary.1`), not in stable `1.4.3`. Pin stable `1.4.3`
+  everywhere and keep ESLint and Prettier, executed by Bun, until a stable
+  release ships them. Then replace them in one change. Until then, user story 5
+  stays open.
+- **Client-only Angular build and a Bun static server.** Angular's production
+  build fails under Bun whenever a server or SSR entry is configured: route
+  extraction loads the server bundle through Node `module.register` loader
+  hooks, which Bun accepts but never applies. Every route is client-rendered
+  today, so the Angular build drops its server and SSR entries and a small
+  `Bun.serve` server delivers static assets with the same cache behavior and
+  falls back to `index.html`. This replaces the agreed Angular web request
+  handler integration and gives up `@angular/ssr`. Adding server rendering later
+  requires revisiting this decision.
+- **Coverage.** `bun test` reports text and lcov with line data only. HTML and
+  Cobertura reports are generated from the lcov with the istanbul report
+  libraries. Branch and function coverage are no longer reported; this
+  reduction is accepted.
+- **Benchmark memory guard.** JavaScriptCore has no `--max-old-space-size`
+  equivalent. The CI benchmark job enforces the limit with a container memory
+  limit instead of a heap-only cap.
+
+**Platform constraints, not project commands:**
+
+- **Gitea actions.** `actions/checkout@v4` (`node20`) and
+  `actions/upload-artifact@v3` (`node16`) are JavaScript actions, so the job
+  container must still provide `node` for the runner. Project commands must not
+  use it.
+- **Allowed hosts.** Found while probing: the current Express server answers 400
+  unless `NG_ALLOWED_HOSTS` is set, and the compose files only set `PORT`. The
+  static Bun server removes this dependency.
+
 ## Testing Decisions
 
 - Test observable behavior and failure outcomes, rather than configuration text