docs(upstream): record the 2026-08-29 T3 review batch and advance the cursor

[rynfar]

Problem

.agents/upstream-review.md had fallen behind integration: an earlier session on 2026-08-29 reviewed f94a0d646..bcb855a63, merged six integration PRs (#164–#169) and opened #170/#171, but never wrote the batch or advanced the cursor. The rest of the range through 1f8ed54ad had then been reviewed and integrated today with no record either.

Fix

Records the full f94a0d646..1f8ed54ad range as one batch: 40 commits, 28 change sets V1–V28, with the earlier session's decisions recovered from PR bodies (V1–V7) and today's decisions and PRs (#181–#188, plus #171 gaining #8624). Advances reviewed-through to 1f8ed54add. Re-checks DEF-7 (still waiting) and opens DEF-8 (#8694, after Expo 57 lands) and DEF-9 (#8693, after file attachments land and upstream settles) with checkable revisit conditions and dates.

Five findings are carried forward in the batch, two of which need a maintainer decision or awareness: the t3 CLI defaults its runtime home to ~/.t3 while the desktop uses ~/.pylon-code, and fs.watch delivers no events on the maintainer's Mac.

Does not add the upstream watch list; PR #173 does that separately and the two should merge cleanly.

Verification

vp fmt --check on the file passes; every table row's column count matches its header; no other batch section changed.

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Claude Fable 5 in Pylon.

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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	13.3 KiB	13.5 KiB	+212 B (+1.6%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	−2 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.6 KiB	+214 B (+3.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	55.5 KiB	57.0 KiB	+1.5 KiB (+2.7%)	66.4 KiB	✅
Codex	Live turn messages	9	11	+2 (+22.2%)	21	✅
Claude	Total thread wire	13.3 KiB	13.3 KiB	−26 B (−0.2%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−10 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−16 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.4 KiB	56.4 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	10	10	0 (0.0%)	21	✅

Baseline: abe70a7 · PR result: 08fde49 · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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