feat(lsp): LSP capability seam, generic stdio provider, and lsp tool

Implements the LSP capability seam RFC as three packages: dsh-lsp (the
ctx.lsp interface — provider registry by branded id + exclusive extension
mapping, per-query order-independent selection, closed request/result
vocabulary, LspError taxonomy), dsh-lsp-local (a generic stdio language-server
provider — Content-Length JSON-RPC framing, per-(provider, workspace) process
single-flight, transient didOpen/query/didClose, an abortable per-instance
queue, UTF-16 negotiation, host-namespace source reads outside ctx.fs, and
bounded shutdown/kill teardown), and dsh-tool-lsp (the model-facing lsp tool —
four operations, one-based UTF-16 cursor conversion, workspace-grouped location
rendering, hover capping, a required session workspace, and a timeout budget).

Why: an agent had text search and file reads but no way to identify a program
symbol — follow an alias, connect an interface to implementations, or read an
inferred type — before changing code. Splitting model contract, seam, and local
subprocess behavior keeps the four semantic queries stable across future remote
or sandbox-native providers without leaking a JSON-RPC escape hatch.

packages/lsp/lsp-local/src/protocol.ts

@@ -0,0 +1,80 @@
+/**
+ * The subset of LSP wire types this generic host reads and writes: initialize capabilities, the four
+ * request results (`Location`, `LocationLink`, `Hover`), and the `textDocumentSync` shapes used to
+ * decide transient-open support. Types only. Fields absent from a real server payload stay optional;
+ * the translation layer normalizes them into the seam's closed unions.
+ * @module @deepseek-ai/dsh-lsp-local/protocol
+ */
+
+/** A zero-based UTF-16 position on the wire (the protocol's `Position`). */
+export interface WirePosition {
+  readonly line: number
+  readonly character: number
+}
+
+/** A wire range (`Range`). */
+export interface WireRange {
+  readonly start: WirePosition
+  readonly end: WirePosition
+}
+
+/** A `Location`: a document URI plus a range. */
+export interface WireLocation {
+  readonly uri: string
+  readonly range: WireRange
+}
+
+/** A `LocationLink`: the target uri plus the selection range to focus. */
+export interface WireLocationLink {
+  readonly targetUri: string
+  readonly targetSelectionRange: WireRange
+  readonly targetRange?: WireRange
+}
+
+/** A `MarkupContent` hover body (`markdown` or `plaintext`). */
+export interface WireMarkupContent {
+  readonly kind: 'markdown' | 'plaintext'
+  readonly value: string
+}
+
+/** A `MarkedString` object form (`{ language, value }`); the string form is a bare `string`. */
+export interface WireMarkedStringObject {
+  readonly language: string
+  readonly value: string
+}
+
+/** One `MarkedString`: a raw string or a language-tagged code block. */
+export type WireMarkedString = string | WireMarkedStringObject
+
+/** A `Hover`: contents in any of the protocol's three encodings, plus an optional range. */
+export interface WireHover {
+  readonly contents: WireMarkupContent | WireMarkedString | readonly WireMarkedString[]
+  readonly range?: WireRange
+}
+
+/** The legacy enum form of `textDocumentSync` (`0` None, `1` Full, `2` Incremental). */
+export type WireTextDocumentSyncKind = 0 | 1 | 2
+
+/** The options form of `textDocumentSync` (`{ openClose, change }`). */
+export interface WireTextDocumentSyncOptions {
+  readonly openClose?: boolean
+  readonly change?: WireTextDocumentSyncKind
+}
+
+/** A `ServerCapabilities.provider` slot: a boolean or an options object (both mean "supported"). */
+export type WireProviderCapability = boolean | Record<string, unknown> | undefined
+
+/** The `ServerCapabilities` fields this host inspects. */
+export interface WireServerCapabilities {
+  readonly positionEncoding?: string
+  readonly textDocumentSync?: WireTextDocumentSyncKind | WireTextDocumentSyncOptions
+  readonly definitionProvider?: WireProviderCapability
+  readonly referencesProvider?: WireProviderCapability
+  readonly implementationProvider?: WireProviderCapability
+  readonly hoverProvider?: WireProviderCapability
+}
+
+/** The `initialize` result envelope. */
+export interface WireInitializeResult {
+  readonly capabilities: WireServerCapabilities
+}