feat: full image support across all channels (#725)

* feat: full image support across all channels

End-to-end image handling: upload, generation, analysis, editing, and
rendering across web gateway, HTTP webhook, WASM (Telegram/Slack), and
REPL channels. Builds on the attachment infrastructure from #596 and
draws inspiration from PR #641's image pipeline approach — credit to
that PR's author for the sentinel JSON pattern and base64-in-JSON
upload design.

Key changes:
- Image upload in web UI (file picker, paste, preview strip)
- Image generation tool (FLUX/DALL-E via /v1/images/generations)
- Image edit tool (multipart /v1/images/edits with fallback)
- Image analysis tool (vision model for workspace images)
- Model detection utilities (image_models.rs, vision_models.rs)
- Sentinel JSON detection in dispatcher for generated image rendering
- StatusUpdate::ImageGenerated → SSE/WS/REPL/WASM broadcast
- HTTP webhook attachment support (base64, 5MB/file, 10MB total)
- WASM channel image download (Telegram via file API, Slack via host HTTP)
- Tool registration wiring in app.rs

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: address PR #725 review comments (16 issues)

- SecretString for API keys in all image tools (image_gen, image_edit, image_analyze)
- Binary image read via tokio::fs::read instead of DB-backed workspace.read()
- Replace Arc<Workspace> with Option<PathBuf> base_dir (workspace has no filesystem API)
- ApprovalRequirement::UnlessAutoApproved for cost-sensitive image tools
- Scope sentinel detection to image_generate/image_edit tool names only
- Skip ToolResult preview broadcast for image sentinels (avoids multi-MB base64 in SSE)
- Extract shared media_type_from_path() to builtin/mod.rs
- Rename fallback_chat_edit → fallback_generate with tracing::warn
- Increase gateway body limit from 1MB to 10MB for image uploads
- Increase webhook body limit to 15MB (base64 overhead)
- Log warning on invalid base64 in images_to_attachments
- Client-side image size limits (5MB/file, 5 images max) in app.js
- aria-label on attach button for accessibility
- Update body_too_large test for new 10MB limit

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: add Slack file size check before download (PR review item #15)

Skip downloading files larger than 20 MB in the Slack WASM channel to
avoid excessive memory use and slow downloads in the WASM runtime.
Logs a warning when a file is skipped. Also bumps channel versions
for Slack and Telegram (prior branch changes).

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* style: cargo fmt

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix(security): add path validation and approval requirement to image tools

Add sandbox path validation via validate_path() to both ImageAnalyzeTool
and ImageEditTool to prevent path traversal attacks that could exfiltrate
arbitrary files through external vision/edit APIs. Also fix
ImageAnalyzeTool::requires_approval to return UnlessAutoApproved,
consistent with ImageEditTool and ImageGenerateTool.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: post-download size guards and empty data_url sentinel check

- Slack: add post-download size check on actual bytes when metadata
  size_bytes is absent, preventing bypass of the 20MB limit
- Telegram: add 20MB download size limit (matching Slack) enforced
  in download_telegram_file() after receiving response bytes
- Dispatcher: skip broadcasting ImageGenerated SSE event when
  data_url is empty from unwrap_or_default(), log warning instead

Closes correctness issues #3, #4, #5 from PR #725 review.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: use mime_guess for media type detection, add alt attrs and media_type validation

- Replace hardcoded media type mapping with mime_guess crate (already in deps)
- Add alt attributes to img elements in web UI for accessibility
- Validate media_type starts with "image/" in images_to_attachments()
- Update bmp test assertion to match mime_guess behavior

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>
Co-authored-by: Zaki <[email protected]>

.gitignore

@@ -23,4 +23,5 @@ bench-results/
 # WASM build artifacts (loaded from disk, not bundled)
 *.wasm
 
+# Traces
 trace_*.json