fix(trim): guard coerceIn to prevent crash on clips shorter than MIN_TRIM_DURATION

[claude]

Summary

Fixes #95

Crash: java.lang.IllegalArgumentException: Cannot coerce value to an empty range: maximum 335 is less than minimum 400 in FilmstripTrimSelector (Crashlytics issue 7169b499fee6554684dba69b1ae1a8f0, first seen v1.0.27).

Root cause: When a clip shorter than MIN_TRIM_DURATION (400 ms) reached the Trim screen, the drag handler and accessibility callbacks called:

// END handle — throws when durationMs < minGapMs
targetMs.coerceIn(curStartMs + minGapMs, durationMs)  // e.g. coerceIn(400, 335)
// START handle — throws when endMs < minGapMs
targetMs.coerceIn(0L, curEndMs - minGapMs)            // e.g. coerceIn(0, -65)

Kotlin's Long.coerceIn throws IllegalArgumentException on inverted ranges.

Fix: Pre-clamp each derived bound so the range is always valid, regardless of clip length:

// END handle
val minMs = (curStartMs + minGapMs).coerceAtMost(durationMs)
val clamped = targetMs.coerceIn(minMs, durationMs)

// START handle
val maxMs = (curEndMs - minGapMs).coerceAtLeast(0L)
val clamped = targetMs.coerceIn(0L, maxMs)

When the clip is shorter than MIN_TRIM_DURATION both handles become immovable, which is correct — the NEXT button is already disabled by trimValid in TrimScreen.kt.

Also: Adds docs/lessons_learned/025-trim-coercein-range-guard-short-clip.md documenting the pattern.

Files changed

File	Change
ui/components/TrimFilmstripControls.kt	Guard all 4 coerceIn calls with inverted-range-safe bounds
docs/lessons_learned/025-trim-coercein-range-guard-short-clip.md	New lesson
docs/lessons_learned/README.md	Index entry for lesson 025

DEFINITION_OF_DONE — steps NOT run on CI

Per docs/DEFINITION_OF_DONE.md, the following could not be verified in this automated triage:

• Release build (./gradlew :app:assembleRelease) — CI has no signing keys
• Emulator run + screenshot — no emulator in this environment; manually launch the Trim screen with a sub-400 ms clip and confirm no crash
• Instrumented tests — not run; no connected device/emulator in CI
• Android Lint clean (./gradlew :app:lintDebug) — not run

Debug build and unit tests should pass in CI.

Manual QA checklist

• Record a very short clip (tap shutter and immediately release, < 400 ms) — confirm no crash on the Trim screen
• Drag both trim handles while on a short clip — confirm handles are immovable (frozen at 0 / durationMs) and no crash
• Use TalkBack / accessibility services to interact with trim handles on a short clip — confirm no crash
• Record a normal clip (≥ 400 ms) — confirm trim handles still work as expected
• Import a short video from gallery — confirm no crash on Trim screen

DRAFT — do not merge. Requires emulator smoke-test and manual QA before marking ready.

[stozo04]

Superseded by #97, which applies the same guard via a pure, JVM-testable TrimHandleMath.kt (all four call sites) and adds a 12-test regression suite verified to reproduce the exact production crash against the unguarded logic. Recommend closing this draft in favor of #97.

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