# @deepseek-ai/dsh-tool-lsp

English | [中文](README.zh.md)

The model-facing **`lsp` tool** over `ctx.lsp`: one read-only tool with four operations for precise code navigation. It owns the model schema, prompt guidance, coordinate conversion, result limits and formatting, and UI presentation; it imports no provider.

Namespace plugin (`name` / `inject` / `Config` / `apply`, no default export). Injects `tools`, `lsp`, and `systemPrompt`.

## The tool

`lsp` accepts `operation` (`goToDefinition` | `findReferences` | `goToImplementation` | `hover`), `file_path`, `line`, and `character`. `line` and `character` are positive, one-based UTF-16 cursor coordinates; the tool converts them to the seam's zero-based positions and converts rendered locations back. `findReferences` includes declarations so impact analysis does not omit the defining site. Provider, language id, workspace root, limits, timeout, initialization, and executable stay outside model input.

The tool requires the workspace root from the session `header.cwd`, with no fallback: absence fails as `LSP_WORKSPACE_REQUIRED` before querying. Its canonical result is the complete normalized Service Definition union: `{ kind: "locations", locations, resolvedWorkspaceUri }` or `{ kind: "hover", hover }`; Code Mode can inspect every acquired location and zero-based range directly. Native rendering projects stable, file-grouped `path:line:character` entries against the provider's canonical workspace URI rather than applying host-platform path rules to the session cwd. A `file:` URI becomes a workspace-relative path inside that URI or a URI-derived absolute path outside it; malformed and non-`file:` URIs stay verbatim. Empty locations and `null` hover are successful no-result responses; malformed provider payloads remain structured errors.

## Configuration

| Key | Default | Meaning |
|---|---|---|
| `maxLocations` | `100` | Largest number of rendered locations before an omission marker. |
| `maxResultChars` | `16000` | Largest complete rendered result, including truncation metadata. |
| `timeoutMs` | `60000` | Tool-call timeout budget, enforced by `dsh-timeout-policy`; covers the complete queued open/query/close lifecycle and is not model-configurable. |

## Model Experience

### System prompt

#### What the model sees

One system-prompt section (order 112) positions LSP as a precision aid with the following text:

##### Verbatim guidance

```markdown
Use search/read for ordinary navigation. Use lsp when textual matches are ambiguous or before a change requires precise definitions, implementations, or references. Positions are one-based line and character (UTF-16) at the cursor; an off-symbol position may return no results. findReferences always includes the declaration.
```

#### Token effect

Fixed guidance cost on every request while the plugin is active.

#### KV Cache effect

Prefix-stable while the plugin scope and guidance text are unchanged; activation or disposal may invalidate reuse from this section.

### Tool schema

#### What the model sees

The model sees the generated [`lsp` schema](../../../docs/tool-catalog.md#deepseek-aidsh-tool-lsp).

#### Token effect

Fixed schema cost on every request while enabled; the `timeoutMs` budget is never sent to the model.

#### KV Cache effect

Prefix-stable while the visible tool definition and order are unchanged; registration lifecycle or scoped restrictions may invalidate reuse from the first changed schema token.

### Results

#### What the model sees

File-grouped `path:line:character` location lines or normalized hover text, capped first by `maxLocations` and then by `maxResultChars`; omission and truncation markers are included inside the complete character cap. These caps affect only Native/model presentation, not the canonical value. Empty results use distinct `No results.` / `No hover information.` lines.

#### Token effect

Capped per tool result by `maxResultChars`, with `maxLocations` additionally bounding navigation item count.

#### KV Cache effect

Tool results append after the cached request prefix and do not directly invalidate it.

### UI presentation

#### What the model sees

Nothing. The client renders a generic search card — `{ card: 'generic', kind: 'search', title, locations: [{ path, line }] }` — whose args-derived title carries the operation and one-based cursor; follow-along focuses the queried line while the title preserves the column.

#### Token effect

Zero direct token effect because rendering is client-side only.

#### KV Cache effect

None; UI presentation is outside the model request.

## Known Limitations and Deferred Work

- **UTF-16 cursor coordinates** — columns are exact for the protocol but hard for a model to count around non-BMP characters; an off-symbol position may return empty results, so the prompt explains the convention without encouraging broad LSP use ([seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-15-lsp-capability-seam.md)).
- **No cross-server completeness promise** — supported servers may return empty or partial results depending on indexing readiness; the tool promises no completeness across languages or servers.
