fix(native-chat): target native chat to the active split leaf

[AmethystLiang]

Summary

Related issue: #8401. Canonical first-flush PR: #8418. This independent follow-up fixes native-chat ownership inside split terminal tabs; it does not change transcript I/O or runtime transport.

Tab-level native-chat actions previously projected whichever pane appeared first, while every split leaf could inherit tab-wide launch metadata. Closing a chat-owning leaf could therefore leave the composer attached to a plain-shell sibling. This PR:

• resolves tab-level agent identity from the active layout leaf instead of pane-map insertion order;
• accepts tab-wide launch/title evidence only while the tab is unsplit;
• keeps chat attached to an eligible chosen leaf and repairs close/reassignment only to an eligible active sibling;
• exits to terminal view when no eligible leaf remains, including mounted and cold-parked tabs;
• makes the shortcut, tab strip, and pane header use the same hydration/layout eligibility rules;
• rejects stale/rootless/nested active-leaf snapshots and clears launch/title identity that belonged to a closed pane.

Screenshots

No visual design change. The behavior is split ownership and close/reassignment routing, covered by deterministic layout and pane-lifecycle regressions.

Testing

• pnpm lint (full lint/custom gates in both passes; changed-file lint rerun after rebase)
• pnpm typecheck (full typecheck in review; web typecheck rerun after rebase)
• Full repository pnpm test was not run; the reviewer passed 12 focused files / 143 tests, then the exact rebased changed-test set passed 69/69
• pnpm build was not run
• Added regressions for mixed splits, insertion order, stale/nested layouts, hydration, shortcut/tab-strip parity, active-leaf changes, mounted closes, parked closes, launch/title cleanup, and plain-shell survivors

AI Review Report

Two separate gpt-5.6-sol xhigh agents implemented and adversarially reviewed the exact branch diff. The second pass found and fixed three high-confidence gaps: stale nested active-leaf acceptance, shortcut/tab-strip hydration divergence, and launch/title evidence leaking from a closed launch-owning pane to a shell survivor.

The review traced layout serialization, active/expanded leaves, selectors, shortcut and tab-strip gates, pane hydration, mounted and parked close paths, title/launch evidence, local versus SSH readability, performance, and overlap with #8418/#8157/#8288. It explicitly checked macOS, Linux, and Windows behavior; no hardcoded shortcut modifier, label, path separator, shell behavior, or platform-specific Electron branch was introduced.

Security Audit

No command execution, filesystem access, IPC/RPC method, dependency, secret, auth, or credential changes. The routing helpers consume existing in-memory layout and pane identity, and the stricter eligibility checks reduce the chance of sending terminal input to a shell pane under the wrong agent identity.

Notes

• Independent of fix(native-chat): retry not-yet-flushed transcripts instead of settling into a permanent error #8418/perf(native-chat): coalesce concurrent transcript reads #8157/fix(codex): resume sessions from authoritative homes #8288 and intentionally excludes transcript transport, paired-host mode, conversation state, composer-send, and accessibility work.
• Residual risk is manual end-to-end validation of rapid pane hydration/close ordering across desktop and SSH hosts.
• X handle: @JinjingLiang

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: c7a7016a-3411-441f-b0c9-a83225bbbabc

📥 Commits

Reviewing files that changed from the base of the PR and between 6f1899b and cd7ef80.

📒 Files selected for processing (2)

• src/renderer/src/components/tab-bar/tab-agent-types-by-tab-id.test.ts
• src/renderer/src/components/tab-bar/tab-agent-types-by-tab-id.ts

🚧 Files skipped from review as they are similar to previous changes (2)

• src/renderer/src/components/tab-bar/tab-agent-types-by-tab-id.ts
• src/renderer/src/components/tab-bar/tab-agent-types-by-tab-id.test.ts

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📝 Walkthrough

Walkthrough

Native chat routing now resolves agents and chat ownership from terminal layout leaves, handles stale or hydating layouts, and restricts tab-wide fallback to safe topologies. Terminal panes use the resolved route and selected launch agent when rendering chat. Pane-close handling now clears launch identity only for the owning PTY and updates tab titles from surviving runtime panes, including parked-tab cleanup. Tests cover routing, fallback safety, active-leaf selection, and close behavior.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 30.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the main change: routing native chat to the active split leaf.
Description check	✅ Passed	The description includes all required sections and covers the main behavior, testing status, review summary, security audit, and notes.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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