Subtask, mission-interview, and milestone/slice-interview sessions could pin
their `generating` state forever when the underlying provider stream stalled
silently or a tool call hung. Wrap each `agent.session.prompt()` in a new
GenerationGuard helper (per-session AbortController + timer) so a stuck turn
becomes a bounded error users can retry. Adds matching `stop*Generation`
exports and threads abort through cleanup so dismissing a modal cancels the
in-flight call instead of leaking it.
Also closes the gh-cli tool hang vector: `runGhAsync` / `runGhJsonAsync` now
accept `{ signal, timeoutMs }` (default 30s). Github-touching extension tools
forward the AI tool's signal so an aborted agent kills the `gh` child instead
of orphaning it.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
