# LSP navigation The LSP seam — a [capability seam](../rfc/implemented/architecture/2026-07-15-lsp-capability-seam.md) exposing semantic code navigation on one `ctx.lsp` service, split across packages: interface ([dsh-lsp](../../packages/lsp/lsp), `ctx.lsp` + the provider registry), a generic implementation ([dsh-lsp-local](../../packages/lsp/lsp-local), a configured stdio language-server host), and consumer ([dsh-tool-lsp](../../packages/lsp/tool-lsp), the `lsp` tool schema). LSP is **one optional capability**, not part of the agent-loop spine — so its vocabulary lives here, not in [core.md](core.md). A provider swap does not change how the model asks for navigation. Source: [`packages/lsp/lsp/src/types.ts`](../../packages/lsp/lsp/src/types.ts) ## Operations and coordinates The seam and model expose exactly four semantic queries; the union is closed, so adding one is a compile-enforced change across the seam, providers, and the tool. Positions and ranges are zero-based UTF-16, matching the protocol; the model-facing tool owns the one-based cursor convention and converts on the way in and out. ```ts type-equiv type LspOperation = 'definition' | 'references' | 'implementation' | 'hover' ``` ```ts type-equiv interface LspPosition { /** Zero-based line. */ readonly line: number /** Zero-based UTF-16 code-unit offset within the line. */ readonly character: number } ``` ```ts type-equiv interface LspRange { readonly start: LspPosition readonly end: LspPosition } ``` ## Request Every field is required: `workspaceRoot` is caller-supplied, `languageId` comes from the provider's registration (not the request), and consumers own timeouts and result limits — so no field needs implementation defaulting and there is no `resolve()` step. The provider receives the caller's request plus the derived `languageId`, which only synchronizes the transient document and never participates in selection. ```ts type-equiv interface LspQueryRequest { /** Which semantic query to run. */ readonly operation: LspOperation /** The source file to query (relative to `workspaceRoot` or absolute; the provider canonicalizes). */ readonly filePath: string /** The zero-based UTF-16 cursor position to query at. */ readonly position: LspPosition /** The workspace root the provider resolves against and indexes; required, never defaulted. */ readonly workspaceRoot: string } ``` ```ts type-equiv interface LspProviderQuery extends LspQueryRequest { /** The LSP language id for `filePath`, from this provider's extension mapping. */ readonly languageId: string } ``` ## Result A CLOSED discriminated union: navigation operations normalize to `locations`, `hover` to content or `null`. Consumers `switch` on `kind` to exhaustiveness so a new arm breaks compilation until handled. `references` always includes declarations — the provider enforces this internally, so callers get no flag. The `locations` variant carries `resolvedWorkspaceRoot`: the provider's canonical form of the request's `workspaceRoot` and the root its `file:` URIs are relative to, so a caller relativizing display paths uses it rather than the possibly-symlinked request root. ```ts type-equiv interface LspLocation { /** The target document URI (`file:` or otherwise), verbatim from the server. */ readonly uri: string /** The range within the target document. */ readonly range: LspRange } ``` ```ts type-equiv interface LspHover { /** The normalized hover text (markdown or plaintext, provider-joined). */ readonly contents: string /** The range the hover applies to, when the server supplied one. */ readonly range?: LspRange } ``` ```ts type-equiv type LspQueryResult = | { readonly kind: 'locations'; readonly locations: readonly LspLocation[]; readonly resolvedWorkspaceRoot: string } | { readonly kind: 'hover'; readonly hover: LspHover | null } ``` ## Provider and service A provider owns a stable branded `id` and an exclusive lowercase leading-dot extension map. `registerProvider` reserves the id and every extension atomically — an invalid or conflicting registration publishes nothing — and its disposer releases all reservations. Selection is per query and order-independent; no match throws `LspError` `LSP_UNAVAILABLE`. The seam exposes no protocol types, process/document controls, or generic JSON-RPC escape hatch. ```ts type-equiv interface LspProvider { /** Stable provider identity, reserved atomically with the extension mappings. */ readonly id: LspProviderId /** Lowercase leading-dot extension → LSP language id (e.g. `{ '.ts': 'typescript' }`). */ readonly extensionToLanguage: Readonly> /** * Run one query. The seam has already selected this provider and derived `languageId`. * @param request - the resolved provider query (caller request + derived language id). * @param signal - optional cancellation; the provider stops its own work when it aborts. * @returns the normalized, closed-union result. */ query(request: LspProviderQuery, signal?: AbortSignal): Promise } ``` ```ts type-equiv interface LspService { /** * Register a provider, atomically reserving its id and every normalized extension. Any conflict * or invalid input publishes nothing and throws `LspError`; the returned disposer releases all * reservations. Disposed with the calling fiber. * @param provider - the backend to register. * @returns a synchronous disposer releasing the id and all extension reservations. */ registerProvider(provider: LspProvider): () => void /** * Select a provider by the file's extension and run one query. Selection is per-query and * order-independent; no match throws `LspError` `LSP_UNAVAILABLE`. * @param request - the normalized query. * @param signal - optional cancellation forwarded to the selected provider. * @returns the normalized, closed-union result. */ query(request: LspQueryRequest, signal?: AbortSignal): Promise } ``` `LspProviderId` is the seam's branded id (`Branded<'LspProviderId'>` from [dsh-brand](../../packages/util/brand)); `LspError` extends `HarnessError` with a stable `code` (`LSP_INVALID_PROVIDER`, `LSP_CONFLICT`, `LSP_UNAVAILABLE`, `LSP_UNSUPPORTED_OPERATION`) callers route on instead of parsing `message`.