feat(lsp+tool-edit-file): multi-server diagnostics + per-edit auto-append

LSP extension:
- Multi-server aggregation: query ALL connected servers matching the
  file's extension (not just the first), merge diagnostics tagged by source
- Incremental sync: capture each server's textDocumentSync.change during
  initialize; compute prefix/suffix diff ranges for change:2 servers;
  full content for change:1 (generic, works for any LSP)
- New diff.ts: pure computeChangeRange + offsetToPosition (O(n), tested)
- Buffer sync: change(filePath, newText) sends didChange with post-edit
  in-memory content; openWithText for first open; tracks open doc text
- languageId mapping: extended with .rb/.rbs/.c/.cpp/etc. (was 'unknown')
- waitForDiagnostics: accepts text override + timeoutMs; returns
  { formatted, slow, timedOut }; polls for publishDiagnostics push
- DiagnosticsStore: hasReceivedPush/clearReceived tracking; formatFiltered
  with minSeverity (1=Error, 2=Warning) for edit_file integration
- LspService.getDiagnostics: service method for cross-extension use

tool-edit-file:
- After successful edit, calls LSP getDiagnostics with post-edit buffer
- Only appends diagnostics with severity ≤ 2 (errors+warnings, no noise)
- Appends slow warning (>10s): 'LSP is taking unusually long...'
- 60s timeout; graceful degradation when no LSP available
- Optional dep on @dispatch/lsp (getService pattern, not manifest depOn)

1468 vitest pass (was 1453, +15 new diff tests).

4 files changed, 74 insertions, 6 deletions

diff --git a/packages/tool-edit-file/package.json b/packages/tool-edit-file/package.json
index f71ad80..7194cce 100644
--- a/packages/tool-edit-file/package.json
+++ b/packages/tool-edit-file/package.json
@@ -6,6 +6,7 @@
 	"main": "dist/index.js",
 	"types": "dist/index.d.ts",
 	"dependencies": {
-		"@dispatch/kernel": "workspace:*"
+		"@dispatch/kernel": "workspace:*",
+		"@dispatch/lsp": "workspace:*"
 	}
 }
diff --git a/packages/tool-edit-file/src/edit-file.ts b/packages/tool-edit-file/src/edit-file.ts
index 36f99e0..1719ea3 100644
--- a/packages/tool-edit-file/src/edit-file.ts
+++ b/packages/tool-edit-file/src/edit-file.ts
@@ -103,13 +103,35 @@ export function computeReplacement(
 	};
 }
 
+// --- Diagnostics hook ---
+
+/**
+ * Optional post-edit diagnostics hook. Returns formatted diagnostics string
+ * (empty if none) + timing metadata. Injected by the extension from the LSP
+ * service; absent when no LSP is available (graceful degradation).
+ */
+export type DiagnosticsHook = (opts: {
+	readonly filePath: string;
+	readonly text: string;
+	readonly cwd: string;
+}) => Promise<{
+	readonly formatted: string;
+	readonly slow: boolean;
+	readonly timedOut: boolean;
+}>;
+
 // --- Shell / edge ---
 
 /**
  * Factory: create an edit_file ToolContract bound to a working directory.
  * The working directory is injected so the tool is testable.
+ * `diagnostics` is optional — when provided, errors+warnings from LSP servers
+ * are appended to successful edit results (only when errors exist).
  */
-export function createEditFileTool(workingDirectory: string): ToolContract {
+export function createEditFileTool(
+	workingDirectory: string,
+	diagnostics?: DiagnosticsHook,
+): ToolContract {
 	const workdir = resolve(workingDirectory);
 
 	return {
@@ -202,7 +224,36 @@ export function createEditFileTool(workingDirectory: string): ToolContract {
 			}
 
 			const plural = result.count === 1 ? "" : "s";
-			return { content: `Replaced ${result.count} occurrence${plural} in "${relPath}".` };
+			let baseContent = `Replaced ${result.count} occurrence${plural} in "${relPath}".`;
+
+			// After a successful edit, query LSP diagnostics (if available).
+			// Only append if there are actual errors/warnings (no noise on clean edits).
+			if (diagnostics) {
+				try {
+					const cwd = ctx.cwd ?? process.cwd();
+					const diag = await diagnostics({
+						filePath: resolvedPath,
+						text: result.content,
+						cwd,
+					});
+					const suffix: string[] = [];
+					if (diag.slow) {
+						suffix.push(
+							"⚠️ LSP is taking unusually long. If this happens more than once, raise it to the user.",
+						);
+					}
+					if (diag.formatted) {
+						suffix.push(diag.formatted);
+					}
+					if (suffix.length > 0) {
+						baseContent += `\n\n${suffix.join("\n\n")}`;
+					}
+				} catch {
+					// LSP diagnostics failure is non-fatal — the edit already succeeded.
+				}
+			}
+
+			return { content: baseContent };
 		},
 	};
 }
diff --git a/packages/tool-edit-file/src/extension.ts b/packages/tool-edit-file/src/extension.ts
index a4bb19e..bbd8256 100644
--- a/packages/tool-edit-file/src/extension.ts
+++ b/packages/tool-edit-file/src/extension.ts
@@ -1,5 +1,6 @@
 import type { Extension } from "@dispatch/kernel";
-import { createEditFileTool } from "./edit-file.js";
+import { lspServiceHandle } from "@dispatch/lsp";
+import { createEditFileTool, type DiagnosticsHook } from "./edit-file.js";
 
 export const extension: Extension = {
 	manifest: {
@@ -13,6 +14,21 @@ export const extension: Extension = {
 		contributes: { tools: ["edit_file"] },
 	},
 	activate(host) {
-		host.defineTool(createEditFileTool(process.cwd()));
+		// Optional LSP integration: if the lsp extension is loaded, wire its
+		// getDiagnostics service as the post-edit diagnostics hook. If absent,
+		// edits proceed without diagnostics (graceful degradation).
+		const lspService = host.getService(lspServiceHandle);
+		const diagnostics: DiagnosticsHook | undefined = lspService
+			? async (opts) =>
+					lspService.getDiagnostics({
+						filePath: opts.filePath,
+						text: opts.text,
+						cwd: opts.cwd,
+						timeoutMs: 60_000,
+						minSeverity: 2, // errors + warnings only
+					})
+			: undefined;
+
+		host.defineTool(createEditFileTool(process.cwd(), diagnostics));
 	},
 };
diff --git a/packages/tool-edit-file/tsconfig.json b/packages/tool-edit-file/tsconfig.json
index ff99a43..38a7610 100644
--- a/packages/tool-edit-file/tsconfig.json
+++ b/packages/tool-edit-file/tsconfig.json
@@ -2,5 +2,5 @@
 	"extends": "../../tsconfig.base.json",
 	"compilerOptions": { "rootDir": "src", "outDir": "dist", "composite": true },
 	"include": ["src/**/*.ts"],
-	"references": [{ "path": "../kernel" }]
+	"references": [{ "path": "../kernel" }, { "path": "../lsp" }]
 }