#18752: Feat(slack): add Canvas content reading support

**## Summary** - **Problem:** OpenClaw cannot read Slack Canvas documents (including Huddle summaries) even with files:read scope - **Why it matters:** Users need to access Canvas content programmatically for automation, context gathering, and Huddle summary parsing - **What changed:** Added read-canvas action using Slack's canvases.sections.lookup API to fetch and parse markdown content - **What did NOT change:** No changes to existing Slack actions, message sending, or file upload functionality **## Change Type (select all)** - [ ] Bug fix - [x] Feature - [ ] Refactor - [ ] Docs - [ ] Security hardening - [ ] Chore/infra **## Scope (select all touched areas)** - [ ] Gateway / orchestration - [x] Skills / tool execution - [ ] Auth / tokens - [ ] Memory / storage - [x] Integrations - [ ] API / contracts - [ ] UI / DX - [ ] CI/CD / infra **## Linked Issue/PR** - [Closes #12601](https://github.com/openclaw/openclaw/issues/12601) ****## User-visible / Behavior Changes**** - New `read-canvas` action available in `message` tool for Slack channels - Requires `canvases:read` scope in Slack app configuration - Returns markdown content extracted from Canvas sections - New config gate: `channels.slack.actions.canvas` (default: enabled) **## Security Impact (required)** - New permissions/capabilities? **Yes** - Secrets/tokens handling changed? **No** - New/changed network calls? **Yes** - Command/tool execution surface changed? **No** - Data access scope changed? **Yes** ****Risk + mitigation:**** - Requires `canvases:read` Slack scope (read-only access to Canvas documents) - Respects existing Slack action gating via `channels.slack.actions.canvas` - Uses existing bot/user token resolution logic (no new auth paths) - Read-only operation, cannot modify or delete Canvases **## Repro + Verification** **### Environment** - OS: Any - Runtime/container: Node.js (OpenClaw standard) - Model/provider: N/A (Slack integration) - Integration/channel: Slack - Relevant config: ```yaml channels: slack: botToken: "xoxb-..." actions: canvas: true **Steps** 1. Add canvases:read scope to Slack app 2. Reinstall app to workspace 3. Call message tool:{ "action": "read-canvas", "channel": "slack", "fileId": "F0AFQP60601" } **Expected** Returns Canvas content as markdown: { "ok": true, "markdown": "# Huddle Notes\n\n- Topic 1\n- Topic 2", "sections": [{"markdown": "..."}] } **Actual** (Will be verified after merge) **Evidence** • [x] Code changes in 3 files (actions.ts, message-actions.ts, slack-actions.ts) • [ ] Test added (TODO: would strengthen PR) • [ ] Verified against live Slack workspace with Canvas documents **Human Verification** • Verified scenarios: Code review, API alignment with Slack documentation • Edge cases checked: Missing sections, empty markdown, missing fileId param • What you did not verify: Live end-to-end test (no dev environment access) **Compatibility / Migration** • Backward compatible? Yes • Config/env changes? No (new opt-in action) • Migration needed? No **Failure Recovery (if this breaks)** • How to disable: Set channels.slack.actions.canvas: false in config • Files to restore: Revert 3 files or disable via config • Known bad symptoms: "Slack canvas reading is disabled" error, or API errors if scope missing **Risks and Mitigations** • Risk: Missing canvases:read scope causes API errors • Mitigation: Clear error message + documented scope requirement • Risk: Large Canvas documents consume excessive tokens • Mitigation: Concatenated markdown returned as single string; caller can truncate if needed