fix(mobile,web): feed and composer fixes, and clearer Pylon Connect removal

[rynfar]

Problem

Three upstream fixes from the #865 catch-up cycle were still missing in Pylon, and the user guide pointed to a mobile screen that does not exist:

• A running thread whose messages were still loading showed only the thinking row, which already counted as "filled", so the feed did not remount and open at the end when the messages arrived.
• On Android foldables the composer dock could keep the unfolded width after resuming folded, because the animated style cleared width instead of assigning it.
• Removing a Pylon Connect environment from a device's connection settings did not say that it stays registered to the account and keeps its host space.
• docs/user/remote-access.md told users to deregister under "Settings → Pylon Connect on mobile"; Pylon mobile has no deregister page.

Fix

• Thread feed: the list mount key treats a thinking-only feed as empty.
• Composer: both layouts assign width explicitly (workspaceContentWidth in split layout, 100% otherwise).
• Connect removal: web shows a dedicated dialog for Pylon Connect environments that links to the account menu's Pylon Connect page; mobile shows a matching alert; the user guide says the same.
• Docs: deregistration now points to the desktop/web account menu and says the mobile app cannot deregister.

Sources

Source	Upstream PR	Disposition
ecd3237b184e87af5d744a9dc28422cc1eb68e1a	#13530	Adopted (clean cherry-pick)
dab9561cae8817bea24442c1dc7e28996de9c52e	#13310	Adopted (clean cherry-pick)
ba79610d166dcc7a9b8beb013d18304bc6261307	#14127	Adapted
525af2d1ad4b6de847ea658c37a081fd7afe8ef6	#13702	Deferred: depends on upstream 151324b2c0bf0ace789820b8ea4ec8ceb55753d9 (#13149, LegendList v2 Home), which Pylon has not adopted
595a1e1f537f403eba408817c2aba35e61c2ac29	#13705	Not applicable, for the same reason

Pylon adaptations

• #14127: all copy says "Pylon Connect". Pylon mobile has no deregister page, so the mobile alert points to the Pylon Connect page in the desktop/web account menu and has no "Open account" button. Existing component file and URL identifiers (T3Connect*, t3-connect) are kept as compatibility names.

Exclusions

• #13702 / #13705: upstream's dormant Home rows and the larger drawDistance are built on a recycling LegendList v2 Home list. Pylon's v2 Home list is a FlatList. No code from either source is in this PR.
• The docs conflict hunk carried an unrelated upstream paragraph about idle tunnel cleanup; only the sentence from #14127 is added.

Verification

• vp test run over apps/mobile/src/features/home, apps/mobile/src/features/threads/threadListV2.test.ts, apps/mobile/src/features/connection, apps/web/src/components/clerk, apps/web/src/components/settings/ConnectionsSettings.logic.test.ts: 18 files, 184 tests passed.
• vp run -F @t3tools/mobile typecheck: ran tsc --noEmit, exit 0. vp run -F @t3tools/web typecheck ran on the earlier head with identical web changes, exit 0.
• vp lint on the changed source files (earlier head): 0 errors, existing warnings only. vp fmt --check: clean.

Limits

No rendered-client pass: no simulator, emulator, device or browser was run. The foldable resume width, the feed remount and the new web dialog (including Clerk's __experimental_startPath) are verified by source review, unit tests and typecheck only.

Refs #865

Model: Claude Opus 5.5. Harness: Claude Code in Pylon. Workflow: review-t3-upstream skill.

[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	14.0 KiB	14.0 KiB	+6 B (+0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.3 KiB	7.3 KiB	−1 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.7 KiB	6.7 KiB	+7 B (+0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.0 KiB	58.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	14.0 KiB	14.0 KiB	−11 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.3 KiB	7.3 KiB	0 B (0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.8 KiB	6.7 KiB	−11 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.9 KiB	58.9 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: da77592 · PR result: b135b00 · 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: 115.7 KiB
• Claude decoded thread snapshot: 116.4 KiB

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