fix(mcp): keep path anchoring when the server has no multiIndexer

[tiendungdev]

Root cause

resolveSymbolID has three rungs: exact hit, cwd-prefix, then graphRelID. The multiIndexer == nil early return sits above the last two — but only the cwd rung actually needs the multi-repo index (it maps a directory to a repo prefix). graphRelID does not, and it was being skipped for free.

Probed on windows/amd64 with the move/inline fixture, which builds its Server through NewServer(...) with no MultiRepoOptions:

multiIndexer == nil:               true
GetNode("pkga/a.go::Foo"):         false
resolveSymbolID("pkga/a.go::Foo")  "pkga/a.go::Foo"   <- returned unchanged
graphRelID("pkga/a.go::Foo")       "pkga\a.go::Foo"
GetNode(graphRelID):               true                <- resolves
graphRelPath("pkga/a.go")          "pkga\a.go"         <- needs no multiIndexer

The machinery was already there and already deliberate — graphPathSpelling's doc-comment names this exact failure:

a forward-slash path — the spelling every agent writes — missed every node below the repo root on Windows and the read tools answered file_not_indexed for an indexed file

The rung was simply unreachable for a server built without MultiRepoOptions.

Change

Scope the guard to the cwd rung. Additive by construction: the graphRelID result stays gated on GetNode(rel) != nil, so it can only turn a miss into a hit — it can never redirect an id that already resolves, and rung 1 still short-circuits an exact match before anything else runs.

Effect

Whole internal/mcp package on windows/amd64, go1.26.6, -count=1:

	failures
main (b8b13ca7)	40
with this change	27

Diffing the failing test names rather than the counts: exactly 13 flip, and the newly-broken set is empty.

FIXED:  TestMoveSymbol_{SamePackage_FunctionRelocated, TargetFileMissing_CreatesIt,
        DryRun_NoOnDiskChanges, CrossPackage_RewritesThirdPartyCaller,
        CrossPackage_CallerInTarget_BecomesBare, CrossPackage_CallerInSource_GainsImport}
        TestInlineSymbol_{TrivialAccessor, TwoCallsites_BothRewritten,
        ArgumentSubstitution, SideEffectArgRefuses, DeleteAfterFalse_KeepsCallee,
        RefusesDefer, RefusesMultipleReturns}
NEWLY BROKEN: (none)

Test

TestResolveSymbolID_WithoutMultiIndexer_StillAnchorsThePath uses an absolute-path id rather than the Windows separator. That exercises the same rung on every platform, so the linux/macos matrix protects this fix and no new windows CI step is needed.

Sabotage-verified: restoring the early return fails both the new unit test (on the anchoring assertion) and TestMoveSymbol_SamePackage_FunctionRelocated; reverting the sabotage returns both to green.

Scope of the user-visible impact — stated narrowly on purpose

The real daemon is not affected: internal/serverstack/shared_server.go:620 passes multiOpts.... The production call sites that build a Server without MultiRepoOptions are cmd/gortex/eval_recall.go:247 and cmd/gortex/eval_server.go:71. So on Windows this cost the eval surfaces their path anchoring, and it cost the test suite 13 tests. I would rather say that plainly than sell it as a broken daemon.

Verification

• golangci-lint run ./internal/mcp/... reports 6 staticcheck SA5011 findings — pre-existing, byte-identical with this change stashed. Untouched here.
• git diff --check clean.

Branched from main at b8b13ca7. Windows 11, go1.26.6.

Related, not included: the remaining 27 windows failures in this package split into symlink-privilege cases (needs SeCreateSymbolicLinkPrivilege, environment rather than code) and further POSIX-spelled assertions, e.g. TestPathToFileURI_Absolute expecting file:///work/main.go where Windows resolves file:///D:/work/main.go. Happy to take those separately if they are worth having.