feat(web): opt-in setting to compact idle threads before sending

[SunkenInTime]

Problem

#15290 made sending a message while the "Resume with less context" banner was showing run /compact first. Users who ignored the banner got their idle threads compacted without asking, and the message they sent sat in the queue behind it. #15771 reverted that. maria asked for it back as an opt-in instead.

The banner itself was Claude-only. #8144 copied Claude Code's own resume prompt (70 minutes idle, 100k tokens), so it only checked for claudeAgent. Nothing about it is Claude-specific: any provider that can run /compact resends the whole stale context on resume.

Change

• The fix(web): sending past the resume banner compacts first #15290 send path is back, gated on a new client setting, compactBeforeResumeEnabled, which defaults to off. With it off, sending past the banner keeps the full history, which matches the banner's "Keep full history" option. The pre-send /compact dispatches as a queued turn, so it never steers into a run that started while the send was being prepared.
• The banner now shows for any provider that offers /compact: Claude, Codex, Grok, OpenCode and Pi. It stays hidden for Cursor and Antigravity. shouldOfferResumeCompaction takes supportsCompaction from the same provider check the Compact button already used, instead of the provider name.
• The toggle is in Settings > General under Follow-up behavior: "Compact idle threads before sending". It's searchable, has a reset button, and is covered by Restore defaults.

Web only. Mobile has no resume banner, and the server is unchanged.

Scope and approval

maria reverted #15290 in #15771 and asked for the behavior back as an opt-in, after Rhys reported /compact running on every stale-thread send in the T3 Code dev Discord. julius asked for it not to be Claude-only.

Verification

Live runs on a worktree dev server, driving the web client with Playwright and Edge. I used real Claude Sonnet 5.5 and Codex GPT-6-Luna threads, each with one turn, then backdated their context snapshots in the worktree's own DB to 150k tokens and 2 hours idle so the banner applies. Each run sends "Reply with exactly the word: back."

Codex, setting on: before this change, the stale Codex thread had no banner (screenshot). Now the banner shows (screenshot), and sending runs /compact first. Codex compacts, then answers the queued message.

Claude, before (main before #15771): /compact runs first and the message waits in the queue.

Claude, setting off (default): the message goes straight to Claude with no /compact.

Claude, setting on: /compact runs first and the message waits in the queue, same as #15290. The Claude banner still shows after the provider change.

Checks: ContextWindowMeter.logic.test.ts (21 passed) and contracts settings.test.ts (159 passed, including a new test for the default-off decode). tsc --noEmit passes for web and contracts. Lint on the touched files shows 0 errors, only warnings that were already there.

Model: Claude Opus 5.5 through Claude Code in T3 Code.

🤖 Generated with Claude Code

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR changes the production send workflow by optionally running a queued /compact turn and broadens the stale-thread banner to additional providers. The setting is default-off, but the provider-scope change and context-mutating workflow are substantial enough to require human review.

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📒 Files selected for processing (1)

• apps/web/src/components/ChatView.tsx

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• apps/web/src/components/ChatView.tsx

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📝 Walkthrough

Walkthrough

Adds a default-off setting that can start a /compact turn before an eligible outgoing message. Adds the setting to Behavior controls, settings search, and restore-defaults handling.

Changes

Compact Before Resume

Layer / File(s)	Summary
Setting contract and controls packages/contracts/src/settings.ts, packages/contracts/src/settings.test.ts, apps/web/src/components/settings/SettingsPanels.tsx, apps/web/src/components/settings/settingsSearch.ts	Adds compactBeforeResumeEnabled with a default of false and patch support. Adds a Behavior switch, search result, and restore-defaults handling. Tests the default and enabling the setting through a patch.
Compact-before-send flow apps/web/src/components/ChatView.tsx	When the setting and eligibility checks allow compaction, onSend starts a /compact turn before the outgoing message and uses queue dispatch. If compaction fails, the outgoing message turn does not start.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Feature

Merge Risk: ⚪ Minimal · up to 06549

The compact-before-send flow does not show an unresolved issue that would block merging after normal checks.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely identifies the opt-in setting to compact idle threads before sending.
Description check	✅ Passed	The description covers the problem, change, scope and approval rationale, and verification. It includes screenshots for the UI change and identifies the model and harness used.

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Inline comments:
Review comments at @apps/web/src/components/ChatView.tsx:
- Around line 9455-9469: Set dispatchMode to queue in the compact turn’s
startThreadTurn call inside onSend, so a run that becomes active during earlier
awaits does not cause /compact to steer.

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📥 Commits

Reviewing files that changed from the base of the PR and between 2188bdd and b2917fe.

📒 Files selected for processing (5)

• apps/web/src/components/ChatView.tsx
• apps/web/src/components/settings/SettingsPanels.tsx
• apps/web/src/components/settings/settingsSearch.ts
• packages/contracts/src/settings.test.ts
• packages/contracts/src/settings.ts

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[juliusmarminge]

i dont like this being a claude only feature and there's no reason for it?

Dismissing prior approval to re-evaluate 7ba79fe