fix(window): preserve scoped session delivery across window transitions

[Juliusolsson05]

A session without a window owner previously broadcast its content to every window. Closing/reloading windows and delayed cleanup could also lose final output or release a newer owner. This change requires an explicit claim for session delivery and makes unrecoverable observation gaps visible in the affected pane.

• Claims carry window-renderer generation and revision. Recovery claims the display only after SessionManager validates the target; stale releases, conflicting-window close requests and obsolete handoff acknowledgements cannot revoke a successor.
• Recognized transition traffic retains an ordered cloned queue under per-session and application item/estimated-byte/age limits. Unknown traffic keeps bounded metadata only. Expired metadata retains conservative evidence in a fixed-size Bloom filter; it never grants routing authority.
• Read-only refresh flushes existing coalescers before seeding available snapshots, then validates owner/run/native-selection/locator evidence around saved-history reads. The real renderer history mapper is reused with stale-update rejection. Refresh preserves drafts and a visible transient-output warning; it never restarts a backend, submits input, or treats a raw PTY tail as a checkpoint.
• Natural backend exit retains pane ownership until explicit disposal. Recorder control edges remain outside the lossy observation queue. Shared history/gap contracts live outside preload, with the old history type re-export preserved.

Validation:

• 116 distinct unit cases across seven focused files: a 114-test serial run passed, then the final two close-admission cases passed with all 15 composed registry/forwarder/IPC cases. Coverage includes the real SessionManager admission path and the existing Codex replacement suite.
• 14 distinct renderer cases across three files: the 13-test run passed, then all eight repair-hook cases passed with the final native-selection case. These exercise the real history mapper and shared header, including late replies, early notices, deduplication and draft preservation.
• Full typecheck and final incremental typecheck passed; test contract, all seven package-pin checks and diff whitespace checks passed.
• npm run test:package passed on the final implementation, including desktop/remote builds, the universal hotkey helper and required-entry-point verification.
• Reviewed the complete diff and all session-routing call sites. Concurrent local tests hit initial dynamic-import timeouts and contaminated subsequent mocks; serial runs passed without increasing timeouts or changing production behavior.

Limits: no live multi-window/PTY smoke was performed. Queue byte limits are admission estimates, not measured heap. Native source evidence uses the current manager's observable fields; unobserved native resets, in-place transcript rewrites and producer epochs across the remaining coalescers are still B12 work under #918. History is a bounded suffix, and missing transient output remains explicit. Runtime archives were not downloaded, so build verification is not a signed-release smoke test. No package pin changed.

Fixes #920
Refs #918

Independent B01 slice of #931, based on 552914f5; does not include or assume merge of tmux PR #933. The focused implementation plan is the branch's first commit. Main subsequently advanced to 115e26fc via the skills/TLDR features; the changed composition lines were inspected and do not overlap this routing wiring. CI must verify the current PR merge revision. Nothing is merged by this PR creation.

CI verification: both quality-gate and minimum-node-fixture-gate passed on head 150328459a6ac392e54070e4a66e4c7d340c2c65, run 34718213663. Review-ready; no merge performed.