live-generate: stop waiting when the dev server dies

A Cursor run reused a dev server another chat had started; that chat's
terminal was reaped mid-session, so the page never reloaded into the
overlay and --wait-for-browser ran out its 60 s budget before the agent
found an error page and restarted the server by hand (about three
minutes lost). The wait now watches the dev URL it knows (the one it
opened, else the boot's, else the caller's hint) with a TCP connect every
third tick; two misses in a row end it with dev_server_gone, whose
instructions name the harness's way to start the dev script and rerun
with --dev-url. generate.md lists the verdict; an integration test kills
a stand-in server mid-wait and sees the verdict inside seconds.

Written with AI assistance (Claude).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/CLI-CONTRACT.md

@@ -1804,7 +1804,7 @@ Conventions: every script's "run directly" guard is `process.argv[1]` ending wit
 - **Invoked from**: `skill/reference/generate.md` (the `generate` command), as the lane's one start command after the agent opened the page in its harness's own browser: `impeccable live-generate --target src/App.jsx --dev-url http://127.0.0.1:5173/ --selector ".pricing-grid" --action bolder --count 3 --boot --wait-for-browser 60000` (`--open` only on a harness with no browser tool; without `--dev-url` and without a wait, the verdict is `browser_needed` and the agent comes back with the page open).
 - **Args**: `--selector <css>` (required), `--text <snippet>`, `--index <n>` (1-based), `--action <name>` (default `impeccable`), `--count <n>` (default 3, 1-8), `--prompt <text>`, `--dry-run`, `--wait-for-browser <ms>`, `--no-live-bar` (body `hideLiveBar:true`: the helper sets its lifetime-wide `hideLiveBar` preference, broadcasts `{type:'live_bar', hidden:true}` to every connected overlay before the target goes out, and answers `hideLiveBar:true` on every later `connected` frame; the overlay hides its global bar accordingly and skips its "No PRODUCT.md found" connect notice, the variant controls still show, and only the helper stopping ends it), `--target <path>` (consumed by `enterLiveRoot`, and the boot's --target under `--boot`), `--boot` (run `live --allow-missing-context --dev-url --no-live-bar [--target]` in-process from the caller's cwd first, reusing a running helper; implies `hideLiveBar:true` on the target; the boot's `devUrl, pageFiles, projectRoot, targetPath, liveBarHidden, contextMissing, contextNote, hasProduct, product, productPath, hasDesign, design, designPath, hasSurfaceBrief, surfaceBrief, surfaceBriefPath` ride along as `boot`; a refusing boot is printed as its own payload plus `ok:false`, `bootError:<its error>` and `_instructions`, exit 1; an unparseable boot → `boot_failed` (+`exitCode`, `detail`)), `--open` (ignored, with `openIgnored:'harness browser'` on the verdict and an `_instructions` prefix saying so, when the provider id is `cursor` or `claude-code` and neither `IMPECCABLE_BROWSER` nor the config's `browser` names a browser: a harness with its own browser never gets a second window from this verb, and the generic `BROWSER` variable is not that choice; otherwise, when `/status` reports no connected client: the dev URL is the boot's `devUrl` or a fresh `dev_url::probe`; none → `no_dev_server`, exit 1; else the URL is opened without waiting for the browser (`IMPECCABLE_BROWSER`, then `browser` in `.impeccable/config.local.json` / `.impeccable/config.json` at the app root, then `BROWSER`, then `open` / `xdg-open` / `cmd /c start`; a value with a path separator runs as a program with the URL as its argument, on macOS any other value is `open -a <name>`), recorded as `opened:{url, via}`, and `--wait-for-browser` defaults to 60000; a launch failure → `browser_open_failed` (+`url`, `detail`)), `--allow-missing-context` (accepted and ignored), `--dev-url [<url>]` (bare: ignored, the boot's own flag; with a value: the dev server the caller already knows, put first in the boot's probe list (`IMPECCABLE_DEV_URL_CANDIDATES` still wins when set) and in this verb's own probe, and reported as `devUrl` with `devUrlVerified:false` when no probe confirmed the tag on it), `--help`. A flag without a value → stdout `{"ok":false,"error":"missing_flag_value","flag":"--x"}`, exit 1.
 - **Env**: `IMPECCABLE_SELF` (how the boot and poll verbs are spelled in `_instructions`).
-- **Behavior**: `enterLiveRoot`; local verdicts first, each pretty-printed JSON on stdout with `_instructions`, exit 1: `selector_required`, `invalid_action` (+`action`, `validActions`), `invalid_count` (+`count`), `invalid_index` (+`index`), `invalid_wait` (+`wait`); no `server.json` (or one without port/token) → `server_not_running`. With `--wait-for-browser`, `GET /status` once a second until `connectedClients > 0` or the budget ends (`no_browser_connected` + `waitedMs`); an unanswered `/status` → `server_unreachable`. Then `POST /agent-target` with `{token, selector, action, count, text?, index?, prompt?, dryRun?}` under a 20 s client cap: a transport timeout → `request_timeout` (+`detail`, browser_timeout instructions), any other transport failure → `server_unreachable` (+`detail`); a non-2xx answer → `{ok:false, error:<body.error or http_<status>>, ...body}`; an unparseable body → `bad_server_response` (+`status`). Before the target goes out, with no page connected (`/status` `connectedClients` 0), no `--open`, no `--wait-for-browser`, and no `--dry-run`: `browser_needed` (`devUrl` from the boot's probe, else a probe led by the hint, else the hint unverified; `devUrlVerified`; `harness`, the provider id) or `no_dev_server` when no URL is known, exit 1. Its `_instructions` name the harness's own browser and never a second one: `cursor` → `browser_navigate` (reuse the tab on that origin); `claude-code` → the Browser pane (`navigate` the tab already on that origin, `tabs_context`, `preview_start` with the URL when the pane is closed); `codex` → rerun with `--open` or give the user the URL; others → the harness browser tool, else `--open` or the user; then rerun with `--wait-for-browser 60000`. `no_dev_server` names where this harness starts a server (`claude-code`: `preview_start` or the dev script; others: the dev script in a background terminal) and asks for `--dev-url <url>` on the rerun. Every verdict from the boot on carries `harness`. A started session (`ok:true`, not a dry run) then collects its own generate event: `GET /poll?types=generate&id=<sessionId>` in ≤5 s slices for up to 20 s, leased exactly as a poll leases it (the preflight scaffold runs on lease), printed as `event` with locally generated `_instructions` (the fast path), or `event:null` when it did not arrive. A 2xx answer is printed as received plus `boot`/`opened` when those ran, plus `_instructions` for `ok` (dry run; started session with `event`, pointing at the edit and at `live-poll --reply <id> done --file <path> --then-poll`; started session without it, pointing at `live-poll` first), `no_dev_server`, `browser_open_failed`, `no_browser_connected` (a variant when `opened` is present), `browser_timeout`, `invalid_selector`, `no_match` (wording depends on `rawMatchCount`), `ambiguous`, `index_out_of_range`, `busy`, `go_failed`, `server_stopping`; exit 0 when `ok:true`, else 1. `_instructions` are regenerated locally from the verdict, never taken from the wire.
+- **Behavior**: `enterLiveRoot`; local verdicts first, each pretty-printed JSON on stdout with `_instructions`, exit 1: `selector_required`, `invalid_action` (+`action`, `validActions`), `invalid_count` (+`count`), `invalid_index` (+`index`), `invalid_wait` (+`wait`); no `server.json` (or one without port/token) → `server_not_running`. With `--wait-for-browser`, `GET /status` once a second until `connectedClients > 0` or the budget ends (`no_browser_connected` + `waitedMs`); while it waits, the dev URL it knows (the one it opened, else the boot's `devUrl`, else the probe or the caller's hint) gets a TCP connect every third tick, and two misses in a row end the wait early with `dev_server_gone` (+`devUrl`, `waitedMs`, `harness`) whose `_instructions` name the harness's way to start the dev script and rerun with `--dev-url`; an unanswered `/status` → `server_unreachable`. Then `POST /agent-target` with `{token, selector, action, count, text?, index?, prompt?, dryRun?}` under a 20 s client cap: a transport timeout → `request_timeout` (+`detail`, browser_timeout instructions), any other transport failure → `server_unreachable` (+`detail`); a non-2xx answer → `{ok:false, error:<body.error or http_<status>>, ...body}`; an unparseable body → `bad_server_response` (+`status`). Before the target goes out, with no page connected (`/status` `connectedClients` 0), no `--open`, no `--wait-for-browser`, and no `--dry-run`: `browser_needed` (`devUrl` from the boot's probe, else a probe led by the hint, else the hint unverified; `devUrlVerified`; `harness`, the provider id) or `no_dev_server` when no URL is known, exit 1. Its `_instructions` name the harness's own browser and never a second one: `cursor` → `browser_navigate` (reuse the tab on that origin); `claude-code` → the Browser pane (`navigate` the tab already on that origin, `tabs_context`, `preview_start` with the URL when the pane is closed); `codex` → rerun with `--open` or give the user the URL; others → the harness browser tool, else `--open` or the user; then rerun with `--wait-for-browser 60000`. `no_dev_server` names where this harness starts a server (`claude-code`: `preview_start` or the dev script; others: the dev script in a background terminal) and asks for `--dev-url <url>` on the rerun. Every verdict from the boot on carries `harness`. A started session (`ok:true`, not a dry run) then collects its own generate event: `GET /poll?types=generate&id=<sessionId>` in ≤5 s slices for up to 20 s, leased exactly as a poll leases it (the preflight scaffold runs on lease), printed as `event` with locally generated `_instructions` (the fast path), or `event:null` when it did not arrive. A 2xx answer is printed as received plus `boot`/`opened` when those ran, plus `_instructions` for `ok` (dry run; started session with `event`, pointing at the edit and at `live-poll --reply <id> done --file <path> --then-poll`; started session without it, pointing at `live-poll` first), `no_dev_server`, `browser_open_failed`, `no_browser_connected` (a variant when `opened` is present), `browser_timeout`, `invalid_selector`, `no_match` (wording depends on `rawMatchCount`), `ambiguous`, `index_out_of_range`, `busy`, `go_failed`, `server_stopping`; exit 0 when `ok:true`, else 1. `_instructions` are regenerated locally from the verdict, never taken from the wire.
 - **Tests**: `tests/oracle/cases/live-generate.mjs` (local verdicts, no-browser), `tests/live-agent-target.test.mjs` (protocol matrix against the binary), `crates/cli/tests/agent_target.rs`, `tests/live-e2e.test.mjs` (`agentTargetScenario`).
 
 #### `live-commit-manual-edits.mjs` -> `impeccable commit-manual-edits`