Enable terminal lifecycle recovery in dogfood

[vorporeal]

Description

Stack PR 8/8; depends on #12858.

Context

The preceding PRs land the coordinator and recovery behavior with TerminalLifecycleRecovery disabled by default. That protects production while the new Precmd completion metadata fields propagate through stable clients, but it also means the recovery path will not receive real-world exercise or diagnostics unless it is enabled for a narrower population first.

Shared-session version skew is the main reason to separate internal enablement from broad rollout: newer viewers recover most reliably once more sharers have reached a stable version that emits the completion metadata added in #12853.

Approach and rollout boundary

This PR enables TerminalLifecycleRecovery only in DOGFOOD_FLAGS. Preview and release defaults remain disabled, so the stack can collect internal telemetry and manual validation without changing behavior for broader channels. Production promotion is intentionally outside this stack and should happen only after the protocol fields have had sufficient stable-release soak time and dogfood diagnostics show the transition policy is behaving as intended.

There are no recovery implementation changes in this PR; it changes only the default audience for the already-gated behavior.

Review guidance

• Is the flag enabled only for dogfood and explicitly absent from preview and release defaults?
• Does this PR avoid changing recovery logic or broadening the rollout beyond the intended internal soak?
• Are the remaining production-promotion criteria clear and intentionally deferred?

Testing

• Added a feature-flag regression verifying recovery is dogfood-enabled but absent from preview and release defaults.
• Final-stack validation: focused lifecycle tests, cargo check -p warp --tests, ./script/format, and git diff --check.

[vorporeal]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Enable terminal lifecycle recovery in dogfood #12859 👈 (View in Graphite)
• Recover missing CommandFinished hooks from Precmd completion metadata #12858
• Safely reconcile repeated and prompt-only Precmd hooks #12857
• Gate terminal lifecycle transitions with a coordinator #12856
• Centralize terminal lifecycle mutations #12855
• Distinguish Precmd hooks with completion metadata from prompt-only hooks #12854
• Add command completion metadata to Precmd #12853
• Document terminal block lifecycle hardening design #12852
• master

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