WIP: LSP integration by terion-name · Pull Request #3118 · coder/mux

terion-name · 2026-04-03T18:54:25Z

In short

This merge request adds a built-in LSP integration to mux. Implementation is heavily inspired by OpenCode LSP architecture. Currently it auto-provisions TypeScript, Python, Go and Rust lsp's. Feature is gated by experiment flag, auto-provisioning is settings-controlled. Multiple runtimes supported.

I did test what I was able to. It would be great if you also take som time to tackle around with it

In details

It introduces:

a backend LSP subsystem managed by mux itself
an agent-facing lsp_query tool for semantic code navigation
automatic post-edit diagnostics after supported structured code changes
a workspace diagnostics API and a minimal Stats → Diagnostics UI
trust-aware, policy-driven provisioning for built-in LSP servers
polling-based diagnostics refresh for already-known files edited outside mux tools
CLI support for the same LSP feature set

The result is that LSP becomes useful in three places at once:

Agent reasoning and code investigations via lsp_query
Agent repair loops via post-edit diagnostics
User inspection via the Diagnostics panel

What this adds

1. Built-in backend LSP subsystem

Mux now owns LSP clients in the backend instead of relying on editor/plugin integration.

2. Agent-facing semantic queries

Adds the experiment-gated lsp_query tool with support for:

hover
definition
references
implementation
document_symbols
workspace_symbols

This gives the model semantic code navigation instead of grep-only exploration.

3. Automatic post-edit diagnostics

After supported structured edits, mux now refreshes LSP state and returns fresh diagnostics in the tool result.

Currently wired into:

file_edit_replace_string
file_edit_replace_lines
file_edit_insert
task_apply_git_patch

This creates a practical edit → diagnose → repair loop for the agent.

4. Workspace diagnostics snapshot + live UI

Adds workspace-scoped diagnostics APIs and a minimal UI surface:

backend:
- workspace.lsp.listDiagnostics
- workspace.lsp.subscribeDiagnostics
frontend:
- Right Sidebar → Stats → Diagnostics

The panel shows:

loading state
retry/error state
empty state
grouped file diagnostics
severity summary
source/code/location metadata

5. Provisioning and trust policy

Adds policy-driven launch/provisioning for built-in servers with config:

lspProvisioningMode: "manual" | "auto"

Built-in policies now cover:

TypeScript
Python / Pyright
Go / gopls
Rust / rust-analyzer

Provisioning is trust-aware:

trusted workspaces can use trusted repo-local execution and auto provisioning
untrusted workspaces cannot use repo-local execution or automatic provisioning

6. Diagnostics refresh after ordinary editor saves

Adds polling-based refresh for already tracked LSP files, so the diagnostics panel can update after out-of-band edits made in an editor or terminal.

This is intentionally scoped:

no whole-repo indexing
no full filesystem watch abstraction
only files already known to the LSP subsystem
polling only runs while diagnostics listeners are active

7. CLI parity

The CLI participates in the same LSP model:

request-scoped lsp-query experiment wiring
effective provisioning mode handling
trust-aware temp-config setup for mux run

Architecture

Backend responsibilities

`LspManager`

Owns orchestration:

descriptor selection
root resolution
client caching/reuse
launch-plan caching
diagnostics caching
publish receipt freshness tracking
idle cleanup
tracked-file polling
query normalization

`LspClient`

Owns protocol interaction:

process startup from a resolved launch plan
initialize / shutdown
didOpen / didChange / didClose
JSON-RPC request/response handling
forwarding publishDiagnostics

`LspStdioTransport`

Owns framed stdio JSON-RPC transport and serialized writes.

Launch policy layer

Launch/provisioning is separated from protocol logic:

lspServerRegistry.ts defines built-in server policies
lspLaunchResolver.ts chooses the final launch plan
lspLaunchProvisioning.ts handles provisioning/probing mechanics

This keeps:

transport
protocol
launch policy
workspace lifecycle

cleanly separated.

Integration points

Service graph / lifecycle

The LSP manager is wired into the backend service graph and workspace lifecycle, so clients are owned and cleaned up by mux.

Relevant files include:

src/node/services/coreServices.ts
src/node/services/serviceContainer.ts
src/node/services/aiService.ts
src/node/orpc/context.ts
src/node/orpc/router.ts

Tool system

lsp_query is added to tool definitions and availability wiring:

src/common/utils/tools/toolDefinitions.ts
src/common/utils/tools/tools.ts
src/common/types/tools.ts
src/node/services/tools/lsp_query.ts

File mutation hooks

Structured file-mutating tools now call a shared onFilesMutated(...) hook, which AIService maps to LspManager.collectPostMutationDiagnostics(...).

Frontend store

Diagnostics snapshots flow through:

src/browser/stores/WorkspaceStore.ts

This store subscribes lazily and exposes diagnostics state to the UI.

Settings / config

Provisioning mode is wired through:

config schema
backend config loading/saving
ORPC
settings UI

CLI

CLI support is wired through:

src/cli/run.ts
src/cli/runOptions.ts
src/cli/runTrust.ts

How it works end-to-end

Explicit agent query

Model calls lsp_query
mux resolves the correct built-in server and root
mux starts or reuses an LSP client
mux syncs file contents if needed
JSON-RPC query runs
mux returns normalized locations/symbols/hover back to the model

Post-edit repair loop

Agent edits code using a supported structured tool
Tool invokes onFilesMutated(...)
AIService asks LspManager for fresh diagnostics
mux re-syncs changed files into the LSP client
mux waits for fresh publishDiagnostics
diagnostics are appended to the tool result

User diagnostics UI

Backend caches diagnostics from publishDiagnostics
ORPC exposes workspace snapshot/subscription
WorkspaceStore subscribes lazily
Stats → Diagnostics renders the current workspace diagnostics state

Built-in server behavior

TypeScript

Supports:

trusted workspace-local typescript-language-server
PATH typescript-language-server
package-manager exec fallback
ancestor TypeScript discovery via tsserver.path
nested package / monorepo handling
fallback provisioning of typescript when needed

Python

Supports:

PATH pyright-langserver
package-manager exec fallback for pyright

Go

Supports:

PATH gopls
managed go install fallback into mux-managed tools dir

Rust

Supports:

PATH rust-analyzer
explicit unsupported error when unavailable

Trust and runtime handling

This MR is intentionally conservative about execution safety.

Trust

LSP launch behavior is driven by:

provisioning mode
trusted vs untrusted workspace execution

Runtime behavior

Launch behavior is runtime-aware:

local/worktree runtimes can safely use sanitized PATH overrides for untrusted pathCommand
remote/container-style runtimes do not get host-local PATH injected
MultiProjectRuntime is unwrapped so trust/path decisions follow its primary runtime behavior

Path mapping

LspPathMapper keeps host/runtime paths aligned so LSP can run inside the runtime environment while mux still reports useful paths to agents and UI.

Known limitations

This MR intentionally does not add:

editor hover / go-to-definition UI
explorer context LSP actions
whole-repo diagnostics indexing
rich diagnostics navigation UI
auto-install support for every ecosystem/runtime combination

The UI surface is intentionally small:

Stats → Diagnostics

The polling refresh is also intentionally narrow:

tracked files only
listener-driven

terion-name · 2026-04-12T14:55:06Z

@ibetitsmike ?

ibetitsmike

Mux working on behalf of Mike.

I found two blocking concurrency issues in the new LSP manager and transport paths. I left both inline below.

ibetitsmike · 2026-04-12T18:05:18Z

+    const client = await this.clientFactory({
+      descriptor,
+      runtime,
+      rootPath,
+      rootUri,
+    });
+    workspaceEntry.clients.set(clientKey, client);


Mux working on behalf of Mike.

If two lsp_query calls hit the same workspace and root concurrently, both callers can observe no existing client here, both await clientFactory(), and the later one overwrites the earlier client in workspaceEntry.clients. That leaks an orphaned LSP process outside manager tracking. Please dedupe in-flight creation per (workspaceId, clientKey) or otherwise serialize this path, then add a concurrent query test that asserts the factory only runs once.

ibetitsmike · 2026-04-12T18:05:18Z

+    const body = this.encoder.encode(JSON.stringify(message));
+    const header = this.encoder.encode(`Content-Length: ${body.byteLength}\r\n\r\n`);
+    await this.stdinWriter.write(header);
+    await this.stdinWriter.write(body);


Mux working on behalf of Mike.

This method writes one LSP frame as two separate awaited writes, header then body. If two requests or notifications share this transport concurrently, the byte stream can interleave as headerA, headerB, bodyA, bodyB, which breaks Content-Length framing. Please serialize writes, or write each framed message in one critical section, and add a concurrent send test for it.

ibetitsmike · 2026-04-13T10:55:00Z

hey @terion-name chatted with the team and I have a good/bad news type of situation.
this work in this work will not land in main. we've noticed the same thing you did - quite a lof of complexity in our code and we're in the process of architecting and implementing a breakdown into a core system + extensions (and moving some of the existing functionalities into those). this would be a great candidate for such. please hop onto our discord and we can have a more direct comms.

in the meantime - you can definitely finish this implementation in your fork and play around with it.

Add shared workspace LSP diagnostics schemas, backend list/subscribe plumbing, browser WorkspaceStore caching/hooks, and focused coverage for manager/store/server paths.

Reconnect active workspace diagnostics subscriptions after client swaps, retry diagnostics streams when they end unexpectedly, and settle pending LSP diagnostic waits during workspace disposal.

Add a Diagnostics sub-tab to the Stats sidebar and render grouped LSP diagnostics from the workspace store without subscribing while the tab is inactive. Add focused tests for the new diagnostics panel states and the Stats sub-tab list.

Separate LSP server metadata from resolved launch plans, add manager-side launch resolution/provisioning helpers, and cover the new seams with focused tests.

Update the policy-context cache-key test to prove trusted workspaces can still use the repo-local TypeScript server while untrusted workspaces fall back to an external PATH entry after workspace-local PATH entries are sanitized.

Poll tracked LSP client files so workspace diagnostics refresh after out-of-band saves. Add a tracked-file accessor to LspClient, start a manager-owned polling loop, and reuse the existing ensureFile/publishDiagnostics path so Stats → Diagnostics updates without UI or ORPC changes. Add focused coverage for tracked-file exposure, empty-cache polling refreshes, and failure tolerance when a tracked file disappears.

Keep poll-driven diagnostics refreshes from looking idle and reset per-workspace poll/serialization bookkeeping on disposal so recreated workspaces do not inherit stale in-flight state.

Search ancestor directories up to the workspace root for TypeScript and package-manager metadata, and provision a fallback TypeScript package when package-manager exec has no usable workspace tsserver.

Ensure untrusted PATH-based LSP resolution always probes and launches with an explicit sanitized PATH.

Separate persisted config reads from the effective runtime config so MUX_LSP_PROVISIONING_MODE stays read-time only, and copy the effective provisioning mode into mux run's ephemeral config.

Keep the sanitized PATH for untrusted pathCommand probing, but stop copying that synthetic env onto the final launch plan unless the launch policy explicitly requested env overrides. Add a regression test covering untrusted pathCommand launches without an explicit env block.

Use the full workspace path when sanitizing untrusted pathCommand PATH entries so nested package roots cannot inherit repo-level node_modules/.bin entries. Also unwrap MultiProjectRuntime to its primary runtime so host-local wrappers still sanitize while Docker/devcontainer-style wrappers keep their remote PATH untouched.

Handle workspace_symbols queries that target a directory like ./ by inferring the matching built-in server from language-specific root markers, skipping file opens when no concrete file is needed, and failing clearly when the directory matches multiple server types.

Prune package-only TypeScript descendants from directory workspace_symbols discovery, warm TypeScript roots with a representative source file before workspace/symbol requests, and summarize repeated root failures so mixed-language monorepos return more useful results.

Prefer exact symbol-name matches when selecting a TypeScript representative file for directory workspace_symbols warm-up, and rank exact path token matches ahead of loose substring matches. Add a repo-root regression test covering the Teleport ResourceService vs ResourcesService case.

Return one workspace_symbols success item per usable directory root, preserve per-root metadata, and surface clearer no-root/no-usable-root failures. Update tool schemas and focused tests to cover the new contract.

Add structured skipped root metadata, richer symbol fields, and disambiguation hints for directory workspace_symbols queries.

Postprocess Go workspace_symbols results so exact symbol-name matches win by default behind EXPERIMENT_LSP_GO_EXACT_MATCH_SYMBOLS, while preserving the original fuzzy output when the env var is explicitly set to false. Add focused coverage for both single-root and directory workspace_symbols queries.

When any directory workspace_symbols root returns an exact match, drop Go-only fuzzy groups unless that Go root also has an exact match. This keeps nested TypeScript exact hits from getting buried under unrelated gopls noise while preserving the existing env-var escape hatch.

terion-name · 2026-04-19T12:28:29Z

hey @terion-name chatted with the team and I have a good/bad news type of situation. this work in this work will not land in main. we've noticed the same thing you did - quite a lof of complexity in our code and we're in the process of architecting and implementing a breakdown into a core system + extensions (and moving some of the existing functionalities into those). this would be a great candidate for such. please hop onto our discord and we can have a more direct comms.

in the meantime - you can definitely finish this implementation in your fork and play around with it.

@ibetitsmike I have pushed implementation to usable state. Tested and tuned on complex multi-language monorepo (like Teleport), fine-tuned behaviors and output shapes for proper agentic understanding.

In general this stuff has a lot of caveats and needs a lot of case-testing. But if we need to wait architectural changes, at this point it doesn't make sense to continue.

It would be great if you in your team also play around with it for some feedback. And when designing extension system to take into consideration this code. Ping me when new arch will be ready, I'll port this

PS
I'll also duplicate this message in discord channel, didn't find you there

lsp integration draft

2dbeafc

ibetitsmike reviewed Apr 12, 2026

View reviewed changes

terion-name added 3 commits April 13, 2026 11:59

address review comments

0fb38f1

Add post-edit LSP diagnostics for mutating tools

115e5f7

Fix post-edit diagnostics freshness and patch file tracking

c11119b

terion-name added 23 commits April 13, 2026 13:55

Fail closed on task_apply_git_patch diff discovery errors

4f4ee43

🤖 feat: add workspace LSP diagnostics snapshots

21781c6

Add shared workspace LSP diagnostics schemas, backend list/subscribe plumbing, browser WorkspaceStore caching/hooks, and focused coverage for manager/store/server paths.

🤖 fix: harden LSP diagnostics recovery

7248bd6

Reconnect active workspace diagnostics subscriptions after client swaps, retry diagnostics streams when they end unexpectedly, and settle pending LSP diagnostic waits during workspace disposal.

fix lsp disposal diagnostics races

7d52175

🤖 feat: add stats diagnostics panel

b43cd80

Add a Diagnostics sub-tab to the Stats sidebar and render grouped LSP diagnostics from the workspace store without subscribing while the tab is inactive. Add focused tests for the new diagnostics panel states and the Stats sub-tab list.

fix diagnostics stats follow-ups

d9dccb3

tests: fix remaining lint issues in LSP/UI tests

ad65e35

🤖 refactor: split LSP launch resolution from client transport

f0b9d6c

Separate LSP server metadata from resolved launch plans, add manager-side launch resolution/provisioning helpers, and cover the new seams with focused tests.

fix lsp launch-plan probing and caching

62bbc24

fix stale LSP launch plan cache on restart

59f8750

Add LSP provisioning policies and config

c1f8a06

fix LSP trust gating and provisioning reuse

dda72e5

Add LSP provisioning setting to GeneralSection

e38f10e

fix: tighten LSP settings persistence

c14cb96

🤖 tests: fix LSP manager trust-gating expectation

fea8e10

Update the policy-context cache-key test to prove trusted workspaces can still use the repo-local TypeScript server while untrusted workspaces fall back to an external PATH entry after workspace-local PATH entries are sanitized.

fix lsp CLI test overrides

7d70cce

Fix mux run trust inheritance for worktree paths

06cba0c

fix lsp diagnostics refresh edge cases

a9e1429

🤖 fix: reset polled LSP workspace refresh state

b380e56

Keep poll-driven diagnostics refreshes from looking idle and reset per-workspace poll/serialization bookkeeping on disposal so recreated workspaces do not inherit stale in-flight state.

🤖 fix: resolve nested TypeScript LSP provisioning

151c555

Search ancestor directories up to the workspace root for TypeScript and package-manager metadata, and provision a fallback TypeScript package when package-manager exec has no usable workspace tsserver.

🤖 fix: harden untrusted LSP pathCommand envs

9fa1dbb

Ensure untrusted PATH-based LSP resolution always probes and launches with an explicit sanitized PATH.

🤖 fix: keep LSP provisioning overrides out of temp and saved config

396f978

Separate persisted config reads from the effective runtime config so MUX_LSP_PROVISIONING_MODE stays read-time only, and copy the effective provisioning mode into mux run's ephemeral config.

terion-name added 20 commits April 16, 2026 23:18

Only poll LSP diagnostics with active listeners

528c91b

Show LSP diagnostics retry state in stats

261e9ba

🤖 fix: keep sanitized PATH for untrusted LSP launches

5072cef

Make LSP path env sanitization runtime-aware

f9df0fe

🤖 fix: prefer deepest workspace_symbols root

d1f2bbb

Merge origin/main into lsp-integration

f13a143

🤖 fix: aggregate directory workspace symbols across roots

64aed6b

Fix TS workspace symbol warm-up root selection

9e961fb

fix TypeScript workspace_symbols warm-up

1968129

🤖 refactor: split workspace symbol roots by directory

521f622

Return one workspace_symbols success item per usable directory root, preserve per-root metadata, and surface clearer no-root/no-usable-root failures. Update tool schemas and focused tests to cover the new contract.

Fix LSP manager test lint assertion

4845c58

🤖 feat: enrich workspace_symbols directory results

e522fe3

Add structured skipped root metadata, richer symbol fields, and disambiguation hints for directory workspace_symbols queries.

Generalize TypeScript LSP project-root selection

e026ba9

Provide feedback

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WIP: LSP integration #3118

WIP: LSP integration #3118
terion-name wants to merge 47 commits intocoder:mainfrom
terion-name:lsp-integration

terion-name commented Apr 3, 2026 •

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In short

In details

What this adds

1. Built-in backend LSP subsystem

2. Agent-facing semantic queries

3. Automatic post-edit diagnostics

4. Workspace diagnostics snapshot + live UI

5. Provisioning and trust policy

6. Diagnostics refresh after ordinary editor saves

7. CLI parity

Architecture

Backend responsibilities

LspManager

LspClient

LspStdioTransport

Launch policy layer

Integration points

Service graph / lifecycle

Tool system

File mutation hooks

Frontend store

Settings / config

CLI

How it works end-to-end

Explicit agent query

Post-edit repair loop

User diagnostics UI

Built-in server behavior

TypeScript

Python

Go

Rust

Trust and runtime handling

Trust

Runtime behavior

Path mapping

Known limitations

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terion-name commented Apr 3, 2026 •

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`LspManager`

`LspClient`

`LspStdioTransport`