Name assistant-generated images even when the plan omits "alt"

[davior]

Problem

Images the assistant generates were showing up in the Assets tab by their UUID filename (022b8a9a-…jpg) instead of a readable name.

Generated files are stored on disk as {uuid}{ext}. The only readable label they get is the image block's name prop, which sync_note_assets copies into NoteAsset.original_name, and the Assets tab shows title or original_name or filename. The executor filled name only from the plan's optional alt field, so any plan without alt left every image named by its UUID.

#202 (per-paragraph placement) added a "Placing blocks" example to the planner prompt that lists section / anchorText / position but no alt, and the image rule only said "Optionally set alt". Batch image plans that follow that example (for example, "an image above every paragraph") come out with no names.

Changes

• backend/app/assistant/executor.py: new image_name(alt, prompt). It uses alt when the plan gives one. Otherwise it takes the image prompt's first sentence, cut at a word boundary to 60 characters. Every generated image block now carries a name.
• frontend/src/services/aiPlan.ts: the planner prompt now asks for alt on every image as a 3–8 word title, and the per-paragraph example includes it. The parser still treats alt as optional.
• Tests: four new executor tests: name from alt, name taken from the prompt, cutting a long prompt, and an end-to-end check that the NoteAsset row gets the name. On the old code, the two fallback tests fail with '' == … and None == ….

Not covered

• Images already registered without a name keep their UUID label, because the blocks have no name or caption to backfill from. They can be renamed in the Assets tab.
• The manual "Generate image" modal still inserts images with no name or caption. That has always been the case, so this PR leaves it alone.

Testing

• pytest tests/test_assistant_executor.py: 62 passed
• vitest run src/services/aiPlan.test.ts: 26 passed
• tsc --noEmit: clean

🤖 Generated with Claude Code

https://claude.ai/code/session_01RSFoSnyUt5dnN1eCnBqi6M

---

Generated by Claude Code