Remove obsolete private language capability constants after catalog migration

[Widthdom]

Problem and priority

P3 — lowest priority in this audit batch. The CLI retains a second set of private language capability names after language matching was delegated to LanguageCapabilityCatalog. Unused declarations add maintenance noise and suggest a source of truth that is no longer used.

Evidence

Observed with a locally built cdidx from origin/main at b52ac0fc372a22eb9667ba409d3d204c153d3188, on macOS, during the 2026-09-05–06 JST dogfood audit. dotnet build passed with zero warnings/errors. Commands below run from the repository root; CLI shorthand means dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll.

unused --actionable --json --limit 15 returns constants in src/CodeIndex/Cli/QueryCommandRunner.LanguageCapabilityConstants.cs:5–14.

The ten names are LanguageCapabilityGraph, LanguageCapabilityReferences, LanguageCapabilitySymbols, LanguageCapabilityMissingGraph, LanguageCapabilityMissingReferences, LanguageCapabilityMissingSymbols, LanguageCapabilitySearchOnly, LanguageCapabilityAll, LanguageCapabilityNone, and LanguageCapabilityMissingAny.

Exact literal navigation with find LanguageCapabilityGraph --all --json --limit 20 found only its declaration and reported complete scanning. QueryCommandRunner.Languages.cs:267–277 delegates capability matching/validation to LanguageCapabilityCatalog. The graph's unused classification alone is not proof of absence.

One-PR scope and implementation guide

• Independently verify each of the ten names with complete locally built cdidx searches, including relevant generated/build inputs or reflection/name consumers before removal.
• Remove only confirmed dead private declarations and the empty partial file if appropriate.
• Preserve the authoritative catalog, accepted capability values, CLI/MCP schemas, shell completions and external behavior.
• Do not refactor unrelated language handling or change the unused heuristic.
• If any declaration is actually used, retain it and explain the evidence; do not force removal to satisfy this issue.

Acceptance and validation

• All removed names are proven unused; no duplicate catalog constants remain in this partial file.
• Build passes, and existing language catalog/parser/completion contract tests on net8.0/net9.0 remain green.
• No new test merely asserting that a source file or constant is absent; use existing behavior tests.
• Follow AGENT_GUIDE.md. This is intended to be behavior-neutral cleanup: document why no user-facing docs/changelog change is needed, unless implementation reveals an actual behavior change.

Prior issues

No exact prior issue was found in targeted searches for these capability constants/catalog. Treat this as maintenance cleanup, not a security vulnerability or a proven regression.

[Widthdom]

Work started on branch fix-issue5262. I will verify all ten private capability constants with the locally built CodeIndex, remove only confirmed unused declarations, and run the existing language contracts and Codex adversarial review.