---
key: session.local-code-intelligence
title: '2026-08-14 — Brief subagents at the csharp-lsp MCP tools; no subagent has been observed to reach the LSP tool (#777)'
status: active
since: '2026-08-14'
supersedes: none
superseded-by: none
rule: 'C# and TypeScript find-all-references are available again; brief delegated agents to the `csharp-lsp` MCP tools (`csharp_references`, `csharp_diagnostics`, …) rather than the `LSP` tool, which no dispatched subagent has been observed to resolve (Claude Code 2.1.232, agent types `general-purpose` and `Explore`, 2026-08-14). Preconditions are machine-local — `env.DOTNET_ROOT` in `.claude/settings.local.json` and a root `node_modules/typescript` link — and checkable with `scripts/check-local-lsp.sh`.'
signals: 'find all references, findReferences, csharp-ls, typescript-language-server, LSP tool, csharp-lsp MCP, libhostfxr, MSBuildLocator, DOTNET_ROOT, subagent tool availability · paths: `docs/local-lsp-tooling.md`, `scripts/check-local-lsp.sh`, `.claude/settings.local.json`, `.mcp.json` · issues: #777, #773, #403, #671'
mechanics: '`docs/local-lsp-tooling.md` — surfaces, configuration, traps, verification'
---

**The capability that would address the residue of Family A was configured, enabled, and dead.** The
population that `testing.guard-derives-population-from-source` cannot reach is the one whose members
are *sites in code* rather than values — #403 (5 of 6 dispatch sites) and #671 (4 of 10 media types).
Find-all-references answers exactly that, and across 811 session transcripts the `LSP` tool was
invoked **zero** times, against 23,661 `Bash` calls over the same corpus. Both C# surfaces failed to
start; nothing reported it, because a language server that cannot initialize is indistinguishable
from one nobody asked.

**Two surfaces, and only one of them has been observed to cross the subagent boundary.** A dispatched
subagent's `ToolSearch` returns "No matching deferred tools found" for `select:LSP` while the same
query resolves in the main session — measured on Claude Code 2.1.232, agent types `general-purpose`
and `Explore`, 2026-08-14, plus the independent §5.1 observation. Three observations on one client
version: design around it, but it is measured behaviour, not a guaranteed contract. The MCP side is
positively evidenced — 326 MCP calls from inside subagent turns across four servers in the transcript
corpus — though not yet for `csharp-lsp` specifically, which only became startable on 2026-08-14. So
the standing note telling *workflow agents* to use C# code intelligence was unsatisfiable as written
against the `LSP` tool, and is satisfiable once pointed at the MCP tools. Naming the surface is the
load-bearing part: an agent that cannot resolve the tool substitutes Grep and does not say so.

**Both failures were a config naming a path the machine does not have.** `MSBuildLocator` needs a
dotnet root owning `host/fxr`, which a Homebrew `bin/dotnet` does not have (`libexec` does); the MCP
entry named a dotnet install that no longer existed, while `~/.codex/config.toml`'s copy of the same
server had been migrated. Neither returned a wrong answer — each refused to start, which is the
benign half of environment divergence and the reason it survived so long.

**`.mcp.json` and `.mcp/` are gitignored, so the working configuration is not recoverable from the
repo.** That is what let one client's copy drift from the other's with nothing to compare against.
`docs/local-lsp-tooling.md` carries the entry verbatim so a second machine can reconstruct it, and
`scripts/check-local-lsp.sh` turns every precondition into a check. The script is deliberately wired
to **no** CI job: every dependency it tests is a developer-machine install, so a red on a runner
would carry no information.

**Rejected: making find-all-references a mandatory step before multi-site fixes.** Not for
availability reasons — C# is *expected* to reach delegated agents through the MCP server, so a
mandate would likely be enforceable there (an inference from the MCP boundary generally, not a
measurement of `csharp-lsp` from a subagent); only the TypeScript route is main-session-bound. The reason is readiness, and it bites each server
separately: `csharp-ls` answers `[]` while `ErsatzTV.sln` loads (minutes), and
`typescript-language-server` answers with the declaration alone while its own project graph loads —
20 references reported as 1, with nothing marking it incomplete. Mandating the step without a way to prove the server had settled would license treating
that answer as a population — the precise failure the step exists to prevent, now carrying the
authority of a rule. It is documented as available and recommended for the multi-site case, with the
re-issue-and-confirm discipline attached, and the zero-invocation baseline above is what a future
measurement should be compared against.