R8a: restore the Key Takeaway and Explainer Note agents

[dovvnloading]

Summary

Restores the two chat-node menu actions that generated a Key Takeaway or an Explainer Note, replacing disabled placeholders with working agents.

Problem

Both menu items rendered as disabled stubs with the tooltip "AI note generation isn't available yet".

That tooltip had been inaccurate since R4. The agent layer it referenced is the same one Regenerate Response, Generate Image and Generate Chart have used ever since. The actual cause was that KeyTakeawayAgent and ExplainerAgent lived in graphlink_agents_core.py, were deleted alongside graphlink_app/ in the R7.6b Qt cutover, and were never ported. No dependency was missing.

Changes

graphlink_note_agent.py restores both agents, carrying over the system prompts, the clean_agent_markdown_response post-processor and the single-chat-call shape verbatim so output matches the previous implementation. Two deliberate divergences, both because the supporting machinery no longer exists:

• No text bounding. The prior implementation routed source text through render_context/source_snapshot, which were removed with the Qt application and have no successor. Every surviving agent path feeds unbounded text, so this matches existing behaviour rather than reintroducing a single bounded path.
• No QThread workers. Concurrency is owned by the dispatcher, so the legacy worker classes have no counterpart.

AgentDispatcher.start_note_generation follows start_chart_generation's directly-awaited shape: the result is a new note node, so the caller requires it within the same round trip and there is no pre-existing node to attach progress state to. A single concurrency guard covers both agents, as they represent the same gesture differing only by prompt; concurrent execution would place two notes at overlapping coordinates. An empty agent response is treated as a failure rather than producing a blank note.

Placement and styling. The note is positioned 400px right of its source node, tinted with the frontend palette's Mid Gray body and Blue header — the closest surviving equivalents to the previous Mid Gray + status_info pairing, as no status_info token exists in the current stack. The previous note width of 400 is not carried over: note width is CSS-driven and not a modeled field.

Source text is the node's own content rather than the branch history generateChart uses; widening it would change what the feature summarises.

The frontend test asserting both items were disabled is inverted rather than removed, as it was the assertion encoding the placeholder as correct.

Verification

Check	Result
Backend suite	1033 passed (12 new)
Frontend tsc --noEmit / ESLint / tests / build	clean / 0 errors / 797 passed (3 new) / succeeds
Qt-free import guard for the new module	passes
Live: both items enabled, no tooltip	confirmed against the running app
Live: click dispatches intent through to the model call	confirmed

Live click-through reached api_provider.chat and surfaced Key takeaway generation failed: Failed to connect to Ollama… because no Ollama instance was running on the verification machine. This exercises the full chain — menu → intent → dispatcher → agent → provider — and confirms the failure path surfaces correctly and creates no node. The success path is covered by unit tests but was not observed against a live model.

Related

Hide Other Branches and Open Document View remain disabled. Both were also lost in the Qt cutover and are tracked as separate work.