fix(mobile): keep native screens ordered during stack pops

[juliusmarminge]

Back transitions in the v5 stack could disturb both the screen and its header. Our retention logic moved the outgoing screen ahead of the root while UIKit was still animating the pop. Fabric child moves can enqueue additional native pop/push operations in the Screens host.

Keep outgoing screens in their previous positions until dismissal finishes, including when another page is pushed immediately afterward. Derive active screens' header back state from router history rather than the retained native child list.

Scope and approval

Requested by Julius after recording broken Settings/Environments transitions. This PR only changes the shared iOS v5 stack's screen retention and header back state, with regression coverage. No Swift or dependency changes; compatible with an OTA on the current native runtime.

Verification

• All 17 stack projection/dismissal tests passed, including Settings pop/re-push and multi-page pop cases.
• Mobile TypeScript check and targeted lint passed.
• React Doctor found no issues in the changed React files.
• Device verification remains pending with Julius. The supplied recording was inspected, but no post-fix visual verification is claimed.

Model: GPT-6.1-sol. Harness: Codex through T3 Code.

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[github-actions]

🚀 Expo continuous deployment is ready!

• Project → t3-code
• Platforms → android, ios
• Scheme → t3code-preview

	🤖 Android	🍎 iOS
Fingerprint	cc64b89b3964de7f7d53a74c3fb993282ba49370	61079c09f769c8f8df76c88c99aac1bfeab50919
Build Details	Build Permalink Details Distribution: INTERNAL Build profile: preview:dev Runtime version: cc64b89b3964de7f7d53a74c3fb993282ba49370 App version: 2.0.0 Git commit: ffd8a3c947cc777817cb1ab936c5e1fa99de1472	Build Permalink Details Distribution: INTERNAL Build profile: preview:dev Runtime version: 61079c09f769c8f8df76c88c99aac1bfeab50919 App version: 2.0.0 Git commit: 35faaa8455f9e2681cbe3a673e0e951ccfec4d83
Update Details	Update Permalink Details Branch: pr-17231 Runtime version: cc64b89b3964de7f7d53a74c3fb993282ba49370 Git commit: 35faaa8455f9e2681cbe3a673e0e951ccfec4d83	Update Permalink Details Branch: pr-17231 Runtime version: 61079c09f769c8f8df76c88c99aac1bfeab50919 Git commit: 35faaa8455f9e2681cbe3a673e0e951ccfec4d83
Update QR

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	4.9 KiB	−23 B (−0.5%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	−23 B (−1.9%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.8 KiB	−41 B (−0.2%)	29.3 KiB	✅
Codex	Live turn messages	2	1	−1 (−50.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	−24 B (−0.5%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	−24 B (−2.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	−41 B (−0.2%)	29.3 KiB	✅
Claude	Live turn messages	2	1	−1 (−50.0%)	8	✅

Baseline: 9a3070b · PR result: dd24df8 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Path: .coderabbit.config.ts
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• Run ID: af751402-f088-48f6-91c5-118162450dd8

📥 Commits

Reviewing files that changed from the base of the PR and between 9a3070b and dd24df8.

📒 Files selected for processing (3)

• apps/mobile/src/native/createV5StackNavigator.ios.tsx
• apps/mobile/src/native/workspace-stack-projection.test.ts
• apps/mobile/src/native/workspace-stack-projection.ts

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 8 remain after this review.

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📝 Walkthrough

Walkthrough

The iOS stack navigator now derives back navigation state from the current route position when attached. Stack reconciliation retains outgoing screens at their prior positions until they are current or native dismissal completes.

Changes

Mobile stack behavior

Layer / File(s)	Summary
Retain outgoing screens in stack order apps/mobile/src/native/workspace-stack-projection.ts, apps/mobile/src/native/workspace-stack-projection.test.ts	Reconciliation inserts outgoing screens at their prior positions, capped at the current list length. Tests cover unfinished pops, immediate pushes, dismissal completion, and multiple outgoing screens.
Derive back state from route position apps/mobile/src/native/createV5StackNavigator.ios.tsx	Attached routes use their index in navigation state to determine back navigation state. Detached routes continue to use their rendered index.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to dd24d

No actionable issue was established in the changed stack behavior. The PR is mergeable after normal checks; device verification remains pending.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: preserving native screen order during stack pops.
Description check	✅ Passed	The description explains the problem, the fix, scope, regression coverage, verification results, and remaining device verification. It does not include a direct issue or approval link, but it provides…
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.

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[macroscopeapp]

Approvability

Verdict: Approved at dd24df8

Macroscope's review found this PR approvable — This is a focused iOS navigation bug fix that preserves native screen order during stack pops and keeps header back-state aligned with the active route. The production changes are limited and supported by targeted regression tests, with no schema, security, billing, deployment, default, or static-analysis impact.

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