Agent crash: an out-of-range integer frame arg (near Int.max) traps Int arithmetic and kills the app

[Ti-03]

The AI agent runs LLM-generated tool calls carrying frame numbers (startFrame, atFrame, toFrame, durationFrames, trim frames). These are only lower-bounded (>= 0 / >= 1), with no upper bound.

An integer near Int.max is finite (so it passes the decode-time finiteness check in decodeToolArgs) and fits in Int (so it decodes cleanly, unlike 1e19, which JSONDecoder rejects when decoding into Int). It then flows into startFrame + durationFrames (Clip.endFrame in Timeline.swift, clearRegion(end:), placeClip). Swift traps on Int overflow, and that trap is not catchable by the do/catch in ToolExecutor.execute, so the whole app crashes instead of returning a tool error.

This is the same failure class as the 1e19 overflow fixed in #201, resurfacing in the tools that were not routed through clampInt.

Reproduction

Via the agent / MCP:

add_clips { entries: [{ mediaRef: <any>, startFrame: 9223372036854775807, durationFrames: 60 }] }

Also reachable via insert_clips (atFrame), move_clips (toFrame), set_clip_properties (durationFrames/trims), add_texts, and apply_layout.

Notes

Confirmed against main (cdd63ff) with a test that drives add_clips at Int.max: the test process is killed with SIGTRAP the moment the tool runs. I have a small, test-backed fix ready if it would be useful.