v0.8.64: Add a dev-server readiness primitive for local app automation

[Hmbown]

Problem

Agents doing local webapp work currently have to poll shell output or guess when a dev server is ready. That makes the loop flaky: npm run dev may print before the app is actually serving, and frontend verification can race the server startup.

The webapp-testing workflow needs a small, reusable readiness primitive that can be used by tools, bundled skills, verifier gates, and helper scripts.

Proposal

Add a bounded dev-server readiness primitive, either as a small native tool, a shared helper, or both.

Initial shape:

• wait for a TCP port to accept connections
• optionally wait for a URL/healthcheck to return a 2xx/3xx response
• support bounded timeout and poll interval
• report structured timeout/connection errors
• work for localhost-first development without requiring a hosted service

This should avoid replacing full process supervision. It is the narrow readiness check that higher-level server lifecycle helpers and browser automation can call.

Acceptance criteria

• A caller can wait for localhost:<port> with a bounded timeout and receive structured success/failure output.
• A caller can optionally wait for an HTTP URL and require a successful status class.
• Timeout output includes the target, elapsed time, and last observed error/status.
• The primitive is usable from the webapp-testing/server-lifecycle flow without ad hoc shell polling.
• Tests cover success, timeout, refused connection, and HTTP non-success behavior using local fixtures.

Related

• v0.9.3: Ship a Playwright-backed browser automation tool #3358 provides browser automation.
• v0.9.3: Bundle webapp-testing skill and server lifecycle helper #3359 bundles the webapp-testing skill and server lifecycle helper.
• v0.9.3: Add visual inspection artifacts for browser and UI tasks #3145 tracks visual artifacts that browser verification can attach.

[Hmbown]

Closing as fixed for v0.8.64. The release branch ships a dev-server readiness primitive as a registered tool: crates/tui/src/tools/dev_server_readiness.rs (registered in tools/registry.rs and the engine tool catalog). Verified on codex/v0.8.64-integration; ships with v0.8.64. Thanks @cyq1017 — PR #3376 implemented exactly this. Reopen if the readiness behavior is off.