menubar: Claude Code/coding-assistant rate-limit monitoring in the menu bar app

[kazukinakai]

Problem / outcome

mindbase/apps/menubar-swift already runs as a native macOS menu bar app (MenuBarExtra +
FSEvents) with health monitoring and an auto-collection toggle, but it has no visibility into
AI coding tool usage/rate limits. Users who already have this app running have no single place
to see how close they are to hitting a rate limit across the coding assistants they use.

Evidence and current behavior

• mindbase/apps/menubar-swift/Sources/MindBaseMenubar/MindBaseMenubar.swift(375 lines)
  implements menu bar residency, health monitoring (URLSession), and an auto-collection toggle.
  No rate-limit/usage/quota display exists (grep -i "rate.limit\|usage\|quota" against this
  file returns zero matches).
• The app already has a ConversationWatcher (FSEvents) monitoring ~/.claude, ~/.cursor,
  and ~/Library/Application Support/Windsurf — i.e. it already knows where these tools keep
  their local state, which is the natural place to also read rate-limit/usage data from.

Reproduction or baseline

Current: swift build --configuration release && ./.build/release/MindBaseMenubar, then opening
the menu shows only health status and the auto-collection toggle — no usage/rate-limit info.

Expected behavior

• The menu bar app's menu shows current rate-limit/usage status for the coding assistants it
  already watches (at minimum Claude Code; extensible to others).
• The data is read from each tool's existing local state (no new login/credential required —
  same local-first philosophy as the rest of the app).
• If a data source is temporarily unreadable, the app does not crash; it shows a clear
  "unavailable" state for that source instead.

Scope

• Add rate-limit/usage display to mindbase/apps/menubar-swift.
• Read rate-limit/usage data from each tool's existing local state files.

Non-goals

• Any change to how conversations are collected/stored (existing ConversationWatcher behavior
  is unchanged).
• Cross-tool routing/optimization logic — this Issue is display-only.

Acceptance criteria

• AC-1: Given the menubar app is running, when the user opens the menu, then Claude Code's
  rate-limit percentage (5h/7d windows) is shown.
• AC-2: Given a rate-limit data source is temporarily unreadable, when the user opens the
  menu, then the app does not crash and shows an explicit "unavailable" indicator for that
  source instead of stale or fabricated data.
• AC-3: The existing health-monitoring and auto-collection-toggle behavior is unchanged after
  this change (no regression).

Verification plan

Criterion	Verification	Expected
AC-1	swift test --package-path mindbase/apps/menubar-swift (new test)	exit 0; rate-limit display logic test passes
AC-2	Same, missing-data-source fallback test	exit 0; no crash
AC-3	Existing test suite under Tests/MindBaseChatTests (or equivalent)	exit 0

Risks, dependencies, rollout

• No dependency on other Issues; this is additive to the existing app.

Clarifications and assumptions

• Assumption: the exact source of rate-limit data (which local file/path per tool) is an
  implementation detail left to the implementer; AC-1/AC-2 verify correctness by observed
  behavior rather than by a specific file path.