perf: move meeting-prompt EKEventStore queries off the main actor

[r3dbars]

Why

MeetingPromptDetector ran synchronous EKEventStore.events(matching:) queries on the main actor: every 20s poll, every supported-app activation, and again on each runtime-prompt dismiss via nextRuntimePromptResumeDate. On large calendars each query blocks the main thread, causing recurring jank in a menubar app that should be invisible.

Product Impact

• Affects: meetings
• Lane: meeting reliability
• Why this matters: prompt detection should never make the whole app stutter every 20 seconds for users with busy calendars.

What changed

• New MeetingPromptCalendarReader owns the EKEventStore and runs queries on a background utility queue, bridged with a checked continuation. The store is never queried on the main thread.
• Each poll cycle does one broad fetch (now-5min .. now+12h, covering both the prompt window and the 12h dismiss-resume lookahead) instead of a narrow query per poll plus ad-hoc 12h queries on dismiss/accept.
• Events are converted to plain-value MeetingPromptCalendarEventSnapshots on the reader's queue (EKEvent objects must not cross threads); only Sendable values hop back to the main actor. This also moves the NSDataDetector meeting-URL scan off main.
• All paths that must stay synchronous — dismiss/remindSoon/markAccepted backoff decisions and currentSuggestedTranscriptTitle() (consumed by MeetingSessionController's sync title closure) — read the main-actor snapshot cache instead of querying live.

Semantics are preserved: the old narrow query window was strictly looser than the shouldOfferCalendarPrompt scoring filter, so cache-derived candidates are identical, and prompt scoring, snooze/pending bookkeeping, and MeetingPromptHeuristics are untouched. Dismiss resume dates read a cache at most one 20s poll stale — a prompt can only be dismissed after the evaluate cycle that refreshed the cache.

How I checked it

• scripts/dev/agent-preflight.sh
• Selected checks from .agents/test-matrix.yml for the files changed (Sources/Meeting/** rule: bash build-deps.sh --force + build + fast tests + integration smoke, all run bare)
• bash build.sh --no-open
• bash run-tests.sh — 4655/4655 passed, warning-free compile; MeetingPromptDetectorTests and MeetingPromptHeuristicsTests green and unmodified
• Performance budget passed (bash build.sh --no-open bundle gate)
• bash run-integration-smoke.sh if I touched Sources/Meeting/ or Sources/TranscriptedCore/
• swift test — not required (no Package.swift / Sources/TranscriptedCore/ changes)
• Manual check: none (no UI change)

Risk Review

• Privacy / local-first behavior reviewed — no off-device payload changes; calendar data stays in-process
• Storage path or migration impact reviewed — none
• Public-facing copy stays concrete and matches current product scope — no copy changes
• Release/update impact reviewed — none
• Agent PRs link the issue/workpad and stay draft until human review
• UI changes include sanitized .agent-review/visuals/ evidence — n/a
• No private transcripts, audio, tokens, personal paths, or customer data are included

Notes

One behavior nuance: currentSuggestedTranscriptTitle() now reads the latest polled snapshot rather than doing a fresh blocking query, so a recording started within the first second after launch (before the first poll lands) could miss the title hint. In exchange, recording start no longer pays a synchronous calendar query.

Agent handoff

COORD_DONE: GREEN | PR URL below | moved MeetingPromptDetector EKEventStore queries to a background reader with a main-actor snapshot cache | none | none | build-deps --force, build.sh --no-open, run-tests.sh (4655 pass), run-integration-smoke.sh | human review + merge

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