[Bug]: the chat agent's text annotation is not fitted to its text, and wraps out of its box in 9:16 #1159

Found during the v2.1.0 release-candidate e2e pass (macOS 26.5 arm64, CI build of release/v2.1.0 @ 9c55596, results row in #1131).

Repro

In the chat panel, in one turn: "add a title 'Demo OpenScreen' from 0:01 to 0:04, then switch the format to vertical 9:16". The agent calls addAnnotation, then setAspectRatio.

Stored annotation

type text, content "Demo OpenScreen", position x 2.33 %, y 45.33 %, size 95.34 % x 9.33 %, fontSize 64, Inter bold, centred, plate rgba(0,0,0,0.7), space "frame".

Actual

In the preview and in the exported 1080x1920 frame at 3.0 s only "Demo" shows; "OpenScreen" wraps onto a second line outside the box.

Expected

The box fitted to the text, as the inspector sizes it, and the title kept on its line across the format change.

Cause

The agent's tools run in the main process, where measureTextBlock (src/lib/ai-edition/annotations/placement.ts) has no OffscreenCanvas and falls back to an average advance of 0.56 em. Inter bold "Demo OpenScreen" at 64 px is 586.5 px wide (hmtx advances of public/fonts/Inter-Bold.ttf); the estimate is 537.6 px. The stored numbers match the estimate exactly: 30.17 % of a 16:9 frame (579 px, leaving 554 px inside the plate for 587 px of words), height 9.33 % (1.25 em line), then scaled by 16/9 / 9/16 to 95.34 % by refitFrameAnnotations, which keeps a text box's shape rather than refitting it. So the box was already too narrow in 16:9, and at 64 px the title cannot fit a portrait frame's width on one line at all (628 px of box for 607.5 px of frame at the reference height).

Platform: all (the measurement runs in the main process on every OS).