fix(clients): preserve review drafts on dismissal

[saphid]

What Changed

Closing review editors could discard unsent text and attachments. Native navigation now protects invested input and transfers comments atomically into the task draft. Web editors retain target-keyed session drafts and original line context across panel dismissal; failed or stale saves cannot clear newer text.

Why

Implements the proposed invariant in pingdotgg#12680. This PR is stacked on that exact documentation branch in the fork; each invariant pair is independent.

Web drafts retain the existing session lifetime. Native back/swipe, attachment transfer, panel reopening and retained line anchors still need real-client proof.

Verification

112 tests across six review/draft-store files passed, including removal immediately after a successful transfer; web/mobile typechecks and targeted lint passed (warnings only).

Independent review: direct SWE-2 Max via Devin, high reasoning requested. Source-only review and a fresh correction review both exited 0. Confirmed findings were fixed and affected checks repeated; remaining conditional findings were checked against the pinned source, with no unresolved actionable defects. The initial tool-based attempt returned no verdict after read commands required confirmation.

UI Changes

Runtime proof (2026-09-20, isolated proof app; base d6f2913 vs this branch): typing a diff-line comment then pressing Cancel discards it silently on base; on this branch a destructive confirm appears ("Discard this comment? Your text has not been added to the draft.").

Before: https://github.com/user-attachments/assets/4f78e941-5004-41f0-8893-461ea5cfb76a
After: https://github.com/user-attachments/assets/ff050741-5128-4628-ae75-02ffa32fbc4a

Only the web diff-comment surface was exercised end to end; the native composer-sheet dismissal path is covered by focused tests — T3 Device tools are unavailable in this environment.

Tracking: https://github.com/saphid/personal-ops/issues/142

Model: GPT-6 Astra via Codex/T3 Code.

[saphid]

Superseded by pingdotgg#12868 — the implementation PR now lives upstream against main (it contains the docs commit until the paired docs PR merges). Same head branch, same commits; this fork draft is closed to avoid a duplicate review surface.