feat(providers): add context compaction across harnesses - #8808

## What's Changed
* feat(desktop): browser profiles for the preview browser by @juliusmarminge in pingdotgg/t3code#7254
* refactor(shared): move the node:sqlite Effect SQL client into shared by @juliusmarminge in pingdotgg/t3code#7272
* feat(web): add opt-in panel animations by @maria-rcks in pingdotgg/t3code#8830
* feat(projects): automatically pull clean default branches by @maria-rcks in pingdotgg/t3code#9277
* fix(web): show pull request state icons in tabs by @flamboh in pingdotgg/t3code#9112
* feat(providers): add context compaction across harnesses by @maria-rcks in pingdotgg/t3code#8808
* feat(web): add proactive panels by @maria-rcks in pingdotgg/t3code#9276
* fix(web): unify control sizing across settings pages by @juliusmarminge in pingdotgg/t3code#9281
* fix(web): offer browser profiles from the empty-panel launcher by @juliusmarminge in pingdotgg/t3code#9279
* Revert "feat(providers): add context compaction across harnesses" by @maria-rcks in pingdotgg/t3code#9284
* fix(web): show scroll-to-end as soon as the last message slips under the composer by @juliusmarminge in pingdotgg/t3code#9280
* fix(cursor): honor auto and full access modes by @maria-rcks in pingdotgg/t3code#9283
* fix(desktop): detect installed Spectre libs for Windows builds by @juliusmarminge in pingdotgg/t3code#9285
* fix(pull-requests): missing features & better behaviour by @maria-rcks in pingdotgg/t3code#9188
* fix(providers): discover workspace skills everywhere by @maria-rcks in pingdotgg/t3code#9180
* fix(server): preserve automatic settlement timestamps by @eimexdev in pingdotgg/t3code#9254
* fix(opencode): show Reasoning selector for OpenCode models by @maria-rcks in pingdotgg/t3code#9287
* feat(web): preview document attachments in the file viewer by @juliusmarminge in pingdotgg/t3code#9292
* chore(ci): narrow the UI consistency check-run agent by @juliusmarminge in pingdotgg/t3code#9297


**Full Changelog**: pingdotgg/t3code@v0.0.39-nightly.20260902.1261...v0.0.39-nightly.20260903.1262

Upstream release: https://github.com/pingdotgg/t3code/releases/tag/v0.0.39-nightly.20260903.1262

Merges 137 upstream commits (`d937e3075..36c4e9c`) into the fork,
following the `fork-upstream-merge` skill. Landed as a merge commit;
conflicts resolved by the inventory's cached verdicts.

## Merge shape

816 files landed (`git diff --stat HEAD^1 HEAD`) against 811 in the
upstream range; fork delta 650 files. The gap of five is all in landed
and not the range: two fork-owned files touched during resolution
(`sandboxControl.placement.test.tsx` test-prop fixup,
`useSandboxCommandsBanner.tsx` reformat) plus the three fork docs this
merge writes (`inventory.json`, `gaps.md`, `upstream-merge-log.md`). No
upstream work was dropped.

## Conflicts

Resolved by inventory verdict — `AGENTS.md` (kept the fork's slimmed
shape, added Antigravity to the provider list), `contracts/rpc.ts` and
`environment.ts`, the ChatView/MessagesTimeline thread-fork +
message-origin convergence, the preview cluster (`addBrowserSurface`
`profileId` beside the fork's `url`, `rightPanelStore` `openAttachment`
beside `retargetFile`), the settings gates, and the two upstream pingdotgg#9364
test deletions.

Two latent fork bugs surfaced and were fixed: `PreviewView`'s hosted
annotation handler called an unexported helper, now routed through the
exported `capturePreviewAnnotationScreenshot` wrapper (matching the
sibling native handler); and `ChatView` passed a `configuredUrls` prop
the fork's hosted `PreviewPanel` does not accept.

## Unsupported methods

`unsupported-methods.mjs` reported ADD 10; recomputed to 0 by adding
`UnsupportedMethodError` to the shared `ProviderSetupRpcError` union
(nine `provider.auth.*` / `provider.install.*` methods) and to
`server.refreshUsageRates`. `gaps.md` grown with a _Provider setup_
bullet and a `refreshUsageRates` clause on _Usage summary_. The three
DROP entries (`scripts.run`, `subtasks.list`, `threads.getShell`) are
the documented keep-anyway exceptions — `apps/server` still refuses
them.

## Feature classification

**Usable as-is** (UI only, no backend dependency): mod+w tab close
(pingdotgg#9363), PageUp/PageDown chat nav (pingdotgg#9315), diff/PR file tree (pingdotgg#9330),
diff-header copy path (pingdotgg#2403), error-report copy (pingdotgg#9166), opt-in
context-window indicator (pingdotgg#9190), opt-in panel animations (pingdotgg#8830),
proactive panels (pingdotgg#9276), button press feedback (pingdotgg#9349), provider-editor
redesign chrome (pingdotgg#8508).

**Unsupported in Moatless** (resolve to a refusal): Antigravity provider
auth/install and all `provider.*` setup (pingdotgg#9348, pingdotgg#8508),
`server.refreshUsageRates`. Desktop-only and already capability- or
desktop-gated, so no new fork work: preview browser profiles (pingdotgg#7254),
open-links-in-app (pingdotgg#9339), ssh-host suggestions (pingdotgg#9171),
environment-as-machine (pingdotgg#9299), continue-threads-across-restart (pingdotgg#9167,
rides the new `serverUpdateThreadContinuation` capability).

**Backend behavior to reproduce** if Moatless wants it: project icons
(pingdotgg#9137, migration 047), auto-pull clean default branches (pingdotgg#9277,
migration 045), inline citations (pingdotgg#9146, needs the backend to emit
them), the usage page. Migration 046
(RepairAutomaticSettlementTimestamps) is upstream-server-only.

Net-zero: context compaction (pingdotgg#8808) landed and was reverted (pingdotgg#9284).

## Verification

`fmt:check`, `lint`, `typecheck`, `tripwires` and `inventory-check`
green. Full test suite green — one web test failed initially
(`addBrowserSurface.test.ts` did not expect the converged default
`profileId`), fixed and re-run.

Two `verify.mjs` checks exit non-zero and are the caveated machine
failures: `unsupported-methods` on the three documented DROP exceptions
above, and `duplicate-adds` on three confirmed false positives
(`openPreview` in a `ChatView` object literal vs its deps array; three
distinct `it()` blocks in `addBrowserSurface.test.ts`).

Written by Claude Opus 5 in Claude Code.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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Moatless task:
https://moatless.soaplabstest.com/tasks/4e881239-73d1-4a93-9563-6a926e920b42