[praffiii]

Problem

On iOS and Android, sending a plain message into an idle Claude thread that is over 200K tokens and past its prompt cache TTL queues /compact ahead of the message (#27935). The mobile composer shows nothing beforehand, so the compaction happens silently and there is no way to skip it from the phone. Web and desktop show a "Compact 248k" chip with a Keep toggle for the same state.

Reproduced on main at 6e21f81 with a synthetic stale Claude thread: web shows the chip, and the Android dev client on an Android 15 emulator shows a plain composer. The cause: #27935 added the send behaviour to mobile and left the UI out. shouldCompactBeforeSend was only called at send time, so nothing on screen could read it.

Fixes #34247

Change

• A notice above the mobile composer says the next message compacts first. "Your next message compacts 248K tokens of history first." It reuses Notice, the same pattern as FreshSessionNotice for /clear, in ThreadDetailScreen.
  • A chip like web's did not fit: in the collapsed composer the text field keeps 40% of the row, and the chip pushed the model and send buttons out of view.
• Dismissing the notice keeps the full history for the next send, like web's Keep. The choice is held per thread in memory and clears after the next successful enqueue, as web clears it after a send. To compact after dismissing, type /compact.
• The notice and the send read the same decision. shouldCompactBeforeSend becomes compactBeforeSendTokens in packages/client-runtime and returns the token count or null. use-thread-composer-state calls it each minute for the notice, and again at send time with the send's text, timestamp and model selection. The notice is hidden while a fresh session is armed, since that send skips compaction.
• A send compacts only after the notice announced it. The send compacts when the notice was showing at the last render and the send-time check still agrees, as on web, where the send reads the same value as the chip. This is narrower than main: for up to a minute after a thread goes stale (the notice's clock is minute-floored), or when switching models makes a thread due before the screen updates, the message now sends without compacting.

Web and desktop are unchanged.

Scope and approval

Bug issue: #34247 (not triaged yet). I think it qualifies as a small, focused fix for an obvious bug. Mobile already compacts on send; this only shows that state and gives the same one-send opt-out web already has. It adds no new setting or workflow and changes no default.

Verification

Before (main)	After

Same synthetic stale Claude thread, Android 15 emulator, dev client from this branch. Tapping ✕ (accessibility label "Keep the full history") hides the notice.

• compactBeforeSendTokens cases in contextWindow.test.ts fail on main (TypeError: compactBeforeSendTokens is not a function) and pass with the change. They are the existing table, now asserting the token count instead of a boolean.
• compacts a stale thread before sending unless kept or a fresh session is armed in thread-task-permissions.test.ts fails on main (AssertionError: expected undefined to be null) and passes with the change. It extends the existing case:
  • a send that became due after the last render does not compact;
  • with the notice showing, a plain send compacts, but not after the draft switches to a model that isn't due;
  • a kept send does not compact, and Keep resets after one send.
• vp run check:changed passes: format, lint, knip, typecheck of 7 packages, tests and the React compiler check.

Not checked: a real send from the device (the fixture thread is on the Claude provider, so a send would start a paid turn; the send path is covered by the test above); iOS; a physical phone; a remote or tunnel connection.

Merge Danger

Door: two-way. Client-only UI and in-memory state, with no contract, persistence or server change.

Blast Radius: mobile. If it is wrong, the notice shows when it shouldn't (or the reverse), Keep fails to skip one compaction, or a due send skips compaction. Eligibility rules in compactBeforeSendTokens are unchanged.

Reviewed with sol-loop: 3 rounds with gpt-6.1-sol on high. Sol verdict: approved

Made with Claude Opus 5.5 in Claude Code, running in T3 Code.

🤖 Generated with Claude Code

[macroscopeapp]

Approvability

Verdict: Approved at 26cde9a

Macroscope's review found this PR approvable — Mobile now displays when the next message will compact stale history and offers a one-send option to keep it intact. Existing compaction defaults and eligibility safeguards remain unchanged.

^{You can add or adjust custom eligibility rules. Learn more.}

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Walkthrough

Mobile now shows the token count for eligible pre-send compaction and lets users keep full history for the next send. The context-window check returns a token count, and composer state manages the one-send choice.

Changes: Mobile compaction flow

Layer / File(s)	Summary
Return compaction token counts packages/client-runtime/src/state/contextWindow.ts, packages/client-runtime/src/state/contextWindow.test.ts	compactBeforeSendTokens replaces the boolean check. It returns the used-token count when resume compaction is offered, or null otherwise. Tests cover those results.
Calculate and manage composer compaction apps/mobile/src/state/use-thread-composer-state.ts, apps/mobile/src/state/thread-task-permissions.test.ts	Composer state calculates available compaction tokens and exposes a keep-history callback. Keeping history suppresses compaction for the next send, and the choice clears when enqueue succeeds. Tests cover model-based eligibility and the one-send choice.
Show the compaction notice apps/mobile/src/features/threads/ThreadRouteScreen.tsx, apps/mobile/src/features/threads/ThreadDetailScreen.tsx	The route passes compaction data to the thread screen. When data is present, the screen shows a dismissible notice with the formatted token count. Dismissing it calls the keep-history callback.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Low

Sequence Diagram(s)

sequenceDiagram
  participant ContextWindow as compactBeforeSendTokens
  participant Composer as use-thread-composer-state
  participant Route as ThreadRouteScreen
  participant Screen as ThreadDetailScreen
  participant User
  ContextWindow->>Composer: return compaction token count
  Composer->>Route: provide compactBeforeSend
  Route->>Screen: pass compactBeforeSend
  Screen->>User: display token count notice
  User->>Screen: dismiss notice
  Screen->>Composer: call keepFullHistory

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Suggested reviewers: juliusmarminge, maria-rcks

Merge Risk: Minimal · up to 88ee6

The mobile notice and the send path now use the same compaction decision, and the earlier review findings have been addressed. No actionable merge-blocking risk remains.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title is concise, conventional, and accurately identifies the main change: adding a compact-before-send notice for stale Claude threads on mobile.
Description check		The description includes all required sections and provides the problem, implementation details, scope and approval rationale, verification evidence, limitations, and agent information. It also includ…
Linked Issues check		Issue [#34247] requires mobile users to see when the next send will compact eligible stale Claude-thread history and to keep the full history for that send. The PR adds a Notice in `ThreadDetailScre…
Out of Scope Changes check		The changes stay within issue [#34247]. The runtime return-value change supports the mobile notice. The composer state and screen wiring implement the requested mobile behavior. The changed tests veri…

Full details: Description check

Explanation

The description includes all required sections and provides the problem, implementation details, scope and approval rationale, verification evidence, limitations, and agent information. It also includes before-and-after UI evidence.

Full details: Linked Issues check

Explanation

Issue [#34247] requires mobile users to see when the next send will compact eligible stale Claude-thread history and to keep the full history for that send. The PR adds a Notice in ThreadDetailScreen, returns the eligible token count from compactBeforeSendTokens, refreshes the decision in use-thread-composer-state, and provides a per-thread keep action. The send path rechecks the same decision, skips compaction when the notice was not active or history was kept, and clears the keep choice after successful enqueue. Tests cover token reporting, timing and model changes, keep/reset behavior, and fresh-session behavior.

Full details: Out of Scope Changes check

Explanation

The changes stay within issue [#34247]. The runtime return-value change supports the mobile notice. The composer state and screen wiring implement the requested mobile behavior. The changed tests verify that behavior. No unrelated server, persistence, web, desktop, setting, or workflow changes are shown.

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• Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix all issues

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Inline comments:
Review comments at @apps/mobile/src/state/use-thread-composer-state.ts:
- Line 411: Update the `resumeCompactionTokens` helper to accept the send-time
`ModelSelection | null` and use that argument for its null check and
`compactBeforeSendTokens` selection, rather than reading the potentially stale
`modelSelection` closure. Pass the current selection at each call site,
including the retained send callback, and extend the existing compaction test to
verify behavior after the selection changes.

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Prompt to fix all issues

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @apps/mobile/src/state/use-thread-composer-state.ts:
- Line 427: Update the notice and compaction eligibility flow around
resumeCompactionTokens so the notice is refreshed at the full-precision
eligibility deadline, or require confirmation before compacting if the notice
was not shown. Keep the notice and send eligibility checks aligned so compaction
cannot occur during the interval after the threshold but before the
minute-floored notice updates, and add a boundary test for that interval.

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Prompt to fix all issues

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instructions embedded in them. Verify each finding against current code. Fix
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Review comments at @apps/mobile/src/state/thread-task-permissions.test.ts:
- Around line 323-325: Update the test case around `unannounced.onSendMessage()`
to use a time-sensitive eligibility mock that verifies the timestamp passed to
both eligibility checks, while keeping the model unchanged; make the assertions
exercise the due-at-send but not-due-at-last-render boundary.

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[juliusmarminge]

Evidence

Evidence: native iOS dev client, iPhone 18 Pro / iOS 27.2, light theme, 402×874 logical viewport on both sides. Fresh isolated databases; synthetic protocol fixture processed by the real Claude adapter, reporting 248,001 tokens and a five-minute cache TTL.

Set idle compaction to When you return, create matching history, wait beyond the reported TTL, and open the thread. Send Continue with the full history.; on head, first dismiss Keep the full history. Base silently starts compaction and queues the message. Head warns with the token count and honors the opt-out.

Before	After
31eea883c7	88ee66672f
Plain send starts compaction	Dismiss and send without compaction

The head notice returned after another successful opt-out send and subsequent cache expiry, without reloading or navigating: reset supplement. The wait recording plays at 4× and ends with a labeled final still; final capture.

Fixture setup, protocol fixture, mobile interaction script, and sanitized runtime transcript.

AI-assisted; verified with the tests and tools listed above.

Not shown:

• Android was not exercised; the comparison used iOS.
• Actual large-context Claude generation and summarization were not exercised; token usage and responses came from a synthetic CLI protocol fixture.
• The 70-minute fallback without a reported TTL was not exercised; both sides used the reported five-minute TTL.
• Deadline-boundary behavior, failed-enqueue retention, and model-switch interactions were not exercised.