docs(upstream): record the 2026-09-02 adoption batch

[rynfar]

Advances the review cursor from 9b2d04317 to beae2147a and records the batch.

Sixteen upstream commits adopted across PRs #241, #242, #246, #248, #249, #251,
#252, #253. Two previously deferred items — #9023 and #8600 — were re-opened
and adopted, since neither deferral rested on a Pylon product decision.

The entry names the carve-outs that recur, and records three defects that tests
caught rather than review, because they are the shape worth expecting: a hunk
that neither applies nor conflicts, an upstream narrowing blind to a fork-only
enum member, and a fork optimization whose premise an upstream rewrite retires.

It also states plainly that 92 upstream commits after the new cursor are
untriaged and have no decision recorded.

Model: Claude Opus 5 in Claude Code.

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[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	13.4 KiB	13.4 KiB	0 B (0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	−1 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.5 KiB	+1 B (+0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.3 KiB	56.3 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	13.4 KiB	13.4 KiB	−7 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−2 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	−5 B (−0.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.2 KiB	57.2 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	8	8	0 (0.0%)	21	✅

Baseline: 9aeaba9 · PR result: 02b204d · 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: 109.5 KiB
• Claude decoded thread snapshot: 110.2 KiB

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