resources-graph: PreToolUse nudge for resources already in memory

[antejavor]

Part of PRD: resources-graph. Vocabulary: context-graph/resources-graph/CONTEXT.md. Prototype reference (throwaway): branch prototype/github-resource-graph-model.

What to build

The Nudge.

• agent-context-graph: a PreToolUse response path (today only SessionStart returns additionalContext), where connectors can contribute one line.
• resources-graph: on a fetch-like tool start, parse the Address, one indexed lookup, on a hit contribute " is in memory, fetched , updated_at — resource returns it". Never deny or modify the call, never call GitHub; any failure → no nudge.
• Verify per harness adapter which can add pre-tool context without denying; others get the session hint only. Document the matrix.

Acceptance criteria

• On Claude Code, fetching an in-memory issue shows the nudge and the fetch still runs.
• Adapter mapping tests for every harness that supports it; unsupported harnesses emit nothing.
• Hook latency stays within existing hook budgets (no network).