Safely reconcile repeated and prompt-only Precmd hooks

[vorporeal]

Description

Stack PR 6/8; depends on #12856.

Context

Precmd is not always a one-time event. Shells can repaint or resend a prompt, and a newer shared-session viewer can receive prompt-only hooks from an older sharer. Re-running the original prompt path against an already populated active block can overwrite command/input state, move the cursor, mutate a finished prompt grid, or repeat once-per-block events. Ignoring every repeat is safer, but it also discards legitimate newer prompt, session, and environment context.

Prompt-only Precmd hooks need a separate policy: they are useful when the model is already safely awaiting or displaying a prompt, but they cannot prove that an executing command completed or identify the next block.

Approach

This PR adds an explicit safe refresh path. A same-active-ID Precmd with completion metadata applies normally when the active block is fresh; if that block already has a prompt, it refreshes the active prompt and context while preserving the current command content, input, and cursor position. A prompt disposition tells downstream dispatch whether this was the first application or a refresh, allowing session/environment state to update without re-emitting public once-per-block prompt events.

Prompt-only evidence is accepted only in the safe prompt phases defined by the coordinator and is ignored elsewhere with diagnostics. It never completes or advances a block. State-mutating repeated-prompt reconciliation remains selected by the recovery gate, while rejection of unsafe prompt-only transitions is unconditional.

Review guidance

• Can a refresh alter command/input content, cursor position, block lifecycle state, or emit completion/prompt side effects a second time?
• Does refreshed context still reach downstream session/environment tracking without a duplicate public Precmd event?
• Is prompt-only evidence restricted to phases where no completion inference is required?

Testing

• Added repeated and prompt-only Precmd coverage for prompt-grid, input, and cursor preservation plus exact once-per-block event counts.
• Added a dispatcher regression proving a refreshed Precmd updates the active session without emitting a duplicate public Precmd event.
• Final-stack validation: 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
• Recover missing CommandFinished hooks from Precmd completion metadata #12858
• Safely reconcile repeated and prompt-only Precmd hooks #12857 👈 (View in Graphite)
• 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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