fix(explore): keep test edges out of the Relationships section

[MohammadBnei]

The problem

On a well-covered symbol, the Relationships section of codegraph_explore is mostly the symbol's own test suite. Asking a real question about a Go store method with a dozen callers:

codegraph explore "What calls sessions.ReserveSlot and where is the live-pod cap maxLive enforced?"

**calls:**
- TestSaveAgentSessionId_StoresTheAgentIdNotTheSessionId → ReserveSlot
- TestReserveSlot_ConcurrentCallersCannotExceedTheCap → ReserveSlot
- killPod → ReserveSlot
- TestDismissStanding_LetsAnExplicitRunGoThrough → ReserveSlot
- TestReserveSlot_ResetsPerPodStateForTheNewPod → ReserveSlot
- TestReserveSlot_ResolvesDecisionsTheDeadPodLeftBehind → ReserveSlot
- TestReserveSlot_CountsAgainstTheCapImmediately → ReserveSlot
- TestSaveAgentSessionID_StaleLeaseCannotClobberTheNewPod → ReserveSlot
- TestArchive_ReleasesTheSlotAndBlocksFurtherReservation → ReserveSlot
- TestSweepQueries_SelectOnlyTheSessionsTheyDescribe → ReserveSlot
- ... and 100 more

Nine of the ten lines are the suite. maxEdgesPerRelationshipKind is small by design, so the production callers — the answer to the question — sit inside "... and 100 more". The section named the test suite instead of the call graph.

The change

Test files are already hard-excluded from the source section for exactly this reason (budget crowding). This applies the same rule one section later, to the edge list.

• Omitted → follows the query, matching what the source-file filter already does, so "which tests cover X" still answers with tests.
• includeTests: true (MCP) / --tests (CLI) → forces them in.
• includeTests: false / --no-tests → forces them out, waiver included.

The waiver regex moved into query-utils as queryIsAboutTests and is now shared with the source-file filter, so the two cannot drift apart on what a test-y query is.

Same query after:

**calls:**
- PromptSession → liveStateOf
- WaitForSessionState → liveStateOf
- DeriveLiveState → IsPodPhaseLive
- DeriveLiveState → humanOriginatedEntry
- CountByRepoLiveState → DeriveLiveState
- enforceStartupStall → ListStartupStalledIDs
...

Blast radius is deliberately untouched. Its tests: line names the covering files rather than flooding a cap — that is the half of this information that was already working, and it stays the way to answer "what covers this?".

Notes for review

• The new test fixture writes 520 filler files because Relationships is gated off below 500 indexed files. Runs in ~5s.
• I did not touch src/mcp/server-instructions.ts. The house rule says to edit it when tool behavior changes, but the new parameter's own schema description is agent-facing and the instructions never mention Relationships or test filtering — happy to add a line there if you'd rather have it.
• CHANGELOG entry added under [Unreleased] → ### Fixes → #### MCP / indexing.

Testing

• __tests__/explore-relationship-test-filter.test.ts — 5 cases: default drops the suite and keeps the production caller, includeTests: true restores it, a test-y query restores it unasked, includeTests: false overrides that waiver, blast radius still names the covering file.
• npx tsc --noEmit clean.
• Full suite on this branch vs. main on the same machine: identical set of 12 failing files (watcher / sync / git-index / worktree — timing-sensitive, unrelated to this change), 39 vs 41 failed tests across two runs, i.e. flake. Everything under explore-*, cli-*, is-test-file, deprioritize-config and context-ranking passes on this branch.

[MohammadBnei]

Follow-up commit — a review pass found three ways the first cut overreached. All three are reproduced output diffs against main, and each has a test that fails on the previous commit.

1. Wrong predicate. It used isTestFile, which is the wide reading — examples, samples, benchmarks and fixtures went with the test suites. Those still render in the Source Code section, so the response contradicted itself, and no phrasing of the query could win them back (queryIsAboutTests doesn't match "which examples call X"). Now isTestPath, which is the "literally a test suite" reading the docstring points at for exactly this case.

2. A pinned test file was erased. extractQueryPaths strips the path span out of matchQuery before the waiver runs, so the "test" inside src/store.test.ts was invisible to it: the file was pinned into the source section and dropped from Relationships in the same response. Pinned files are now exempt, matching the source-file filter's own exemption.

3. The section could vanish outright. With no non-test callers there was nothing left to render. The source filter stands down in that case ("tests are the only signal for this area") and the blast radius does not cover for it — that section is roots-only, capped at 5, and MEANINGFUL-kinds-only, so a non-root symbol whose callers are all tests lost the information entirely. It now stands down too. An explicit includeTests: false still means false: that caller asked for the empty section.

Test file is up to 9 cases; the three new ones fail on the previous commit and pass on this one. tsc --noEmit clean, sibling explore suites + is-test-file + deprioritize-config all pass (65 tests).