perf(mobile): preserve Markdown views while streaming

[t3dotgg]

Streaming Markdown used growing end offsets and text in React keys. Each update could replace the active text view, code block, and scroll container.

Keep block keys tied to type and start position. Keep text-run and code-token keys stable as content grows. Formatting and block-type changes still get separate identities.

Checked:

• 49 focused Markdown tests passed.
• Mobile typecheck, targeted lint, and formatting passed. Two existing React lint warnings remain in the code-block renderer.
• The locked C++ parser confirmed stable keys for prose, open and closed fences, tables, nested code, and completed blocks. A paragraph-to-heading change gets a new key.

No browser or device testing, as requested. Selection, copy feedback, and horizontal scrolling have source checks only. No native source or configuration changed.

Merge hold: CI detects an iOS fingerprint change because Expo hashes the whole local Markdown module. This needs a native-release merge window under the current fingerprint policy.

Part of the performance audit.

Created with GPT-6 Astra (preview) in Codex.

[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	13.5 KiB	13.7 KiB	+237 B (+1.7%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−3 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.7 KiB	+240 B (+3.6%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	58.5 KiB	+1.5 KiB (+2.6%)	66.4 KiB	✅
Codex	Live turn messages	8	10	+2 (+25.0%)	21	✅
Claude	Total thread wire	13.7 KiB	13.6 KiB	−158 B (−1.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	+1 B (+0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.6 KiB	−159 B (−2.3%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	59.3 KiB	57.9 KiB	−1.4 KiB (−2.4%)	66.4 KiB	✅
Claude	Live turn messages	10	10	0 (0.0%)	21	✅

Baseline: caa8a0d · PR result: 36318af · 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: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

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

[macroscopeapp]

Approvability

Verdict: Approved at 36318af

Macroscope's review found this PR approvable — The PR narrowly stabilizes iOS Markdown component identities during streaming, preserving existing text, code, and block views while still remounting when rendering attributes or node types change. The implementation is covered by focused tests and introduces no schema, deployment, security, billing, or product-default changes.

^{You can add or adjust custom eligibility rules. Learn more.}

[juliusmarminge]

Superseded by #11211 (perf(mobile): reuse completed code lines while streaming), which landed the stable Markdown sibling keys (offset:<beg> / index:<i>) plus incremental completed-line highlight reuse on main. Closing this older native-hold PR as wash leftover hygiene.

[juliusmarminge]

Closed as superseded by #11211.