perf(web): preserve Markdown controls while messages stream

[rynfar]

Streaming text recreated Markdown renderer component types, resetting controls and repeating syntax highlighting. Keep those renderers mounted and pass current message state through React context. A failed highlighter retries when its inputs change while retaining code-block controls.

Ports upstream #9677, 887ece307131bdc853cc10f3b82067dee77c4ecf, plus the Markdown recovery slice of #9799, ce4712d5b04fb998f79fe132245289191147e5d5. Keeps Pylon’s editor availability, click-time editor preference, external-link behavior, long-link wrapping, and video expansion. No upstream renderer body replaces those behaviors.

Validation: 55 real React and Markdown tests pass, including persistent wrap/copy/details state, current task edits, one highlight call across ten unchanged-fence updates, and recovery from a highlighter failure. Web typecheck and scoped lint pass.

In the disposable browser app, expanded Markdown details and code wrapping survived 90 synthetic streaming updates. An ongoing-stream focus check retained the same connected, focused code control. The baseline collapsed expanded details. Integrated client validation passed 454 focused tests and three client typechecks.

Before	After

Before navigation/streaming clip · After navigation/streaming clip.

Model: GPT-6 Astra. Harness: 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	13.7 KiB	13.7 KiB	−49 B (−0.3%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	+2 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.6 KiB	6.6 KiB	−51 B (−0.8%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.3 KiB	56.5 KiB	−778 B (−1.3%)	66.4 KiB	✅
Codex	Live turn messages	8	9	+1 (+12.5%)	21	✅
Claude	Total thread wire	13.7 KiB	13.7 KiB	+71 B (+0.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−7 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.6 KiB	+78 B (+1.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.3 KiB	58.1 KiB	+840 B (+1.4%)	66.4 KiB	✅
Claude	Live turn messages	8	8	0 (0.0%)	21	✅

Baseline: a438388 · PR result: b302f53 · 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: 111.2 KiB
• Claude decoded thread snapshot: 111.9 KiB

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