resources-graph: tracer bullet — single issues, PRs and repos served from memory

[antejavor]

Closes #465. First slice of PRD: resources-graph: an agent reads a public GitHub issue, PR or repository; a later read is served from memory.

What's in it

New context-graph/resources-graph package:

• Address parser (pure): WebFetch URLs, gh issue|pr|repo view, gh api repos/..., curl to api.github.com, GitHub MCP tools, prompt links and owner/repo#n → normalised Addresses. gh without -R is skipped (the repo would come from the cwd).
• Connector: tool starts → FETCHED Touches, user prompts → PROMPTED Touches, finished resource calls → Cache Reads. No network in hooks.
• Sweep (resources-graph sweep): pending Touches → Resources via GraphQL, public-only, items resolved by issueOrPullRequest(number), comments/files/review threads paged to the end; failures kept as Unresolved Touches (not_found / not_public / rate_limited). FETCHED Touches refetch; PROMPTED ones of stored Resources just resolve.
• resource tool: served by agent-context-graph mcp; returns content + fetched_at + updated_at, never calls GitHub, writes nothing.

Credentials: the Sweep fetches with the user's own gh login (gh auth token) — the access the agent already reads GitHub with — so most users configure nothing. github.token in the config file is an optional override that wins when set (amends the capture-model decision, see #457).

agent-context-graph: github.token config key (secret, survives bootstrap), --connector resources-graph in the runner and schema setup, doctor check.

Decisions worth a look

• Cache Reads are recorded by the connector, not the tool: the MCP tool can't see the session. The tool's answer starts [resource hit|miss] <address>; the connector records the Cache Read from the post-tool event.
• Moved resources (renamed repo, transferred issue): the Touch resolves to the Resource's new Address; the old holder loses the Address.
• An item's Repository is always fetched and stored with its README first — no content-less Repository nodes.
• sessions-graph is a test-only dependency so privacy tests use the real owner of (:User)-[:HAD_SESSION].

Testing

• 69 tests on a real Memgraph (./scripts/dev-memgraph.sh test resources-graph): unit tests for the parser and the GitHub source; e2e for read-twice, private Touches / shared Resources, PR via /issues/N, refetch dropping deleted comments, unresolved reasons, idempotent hook re-delivery; token resolution (gh login, override, logged out, no gh); the real hook run claude-code path. GitHub is replayed from responses recorded on memgraph/memgraph (tests/fixtures/record.py), plus one live test when GITHUB_TOKEN is set.
• agent-context-graph: 167 pass.
• Dogfooded against live GitHub with a throwaway config: hook payloads → Touches → resources-graph sweep → resource hit/miss through the MCP tool registry; and a Sweep with no github.token configured, fetching with the gh login.

The README links CONTEXT.md, which arrives with #461.