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).

1 files changed, 26 insertions, 2 deletions

diff --git a/packages/lsp/src/diagnostics.ts b/packages/lsp/src/diagnostics.ts
index ea18811..bc7ac0a 100644
--- a/packages/lsp/src/diagnostics.ts
+++ b/packages/lsp/src/diagnostics.ts
@@ -34,9 +34,11 @@ const severityNames: Record<number, string> = {
 export class DiagnosticsStore {
 	private pushDiagnostics = new Map<string, readonly Diagnostic[]>();
 	private pullDiagnostics = new Map<string, readonly Diagnostic[]>();
+	private pushReceived = new Set<string>();
 
 	setPushDiagnostics(params: PublishDiagnosticsParams): void {
 		this.pushDiagnostics.set(params.uri, params.diagnostics);
+		this.pushReceived.add(params.uri);
 	}
 
 	setPullDiagnostics(uri: string, report: DocumentDiagnosticReport): void {
@@ -45,14 +47,32 @@ export class DiagnosticsStore {
 		}
 	}
 
+	/** True if the server has pushed at least one publishDiagnostics for this URI. */
+	hasReceivedPush(uri: string): boolean {
+		return this.pushReceived.has(uri);
+	}
+
+	/** Clear the "received" flag so the next waitForDiagnostics poll detects fresh pushes. */
+	clearReceived(uri: string): void {
+		this.pushReceived.delete(uri);
+	}
+
 	getMerged(uri: string): readonly Diagnostic[] {
 		const push = this.pushDiagnostics.get(uri) ?? [];
 		const pull = this.pullDiagnostics.get(uri) ?? [];
 		return dedupeDiagnostics([...push, ...pull]);
 	}
 
-	format(uri: string): string {
-		const diags = this.getMerged(uri);
+	/**
+	 * Format diagnostics for a URI, optionally filtering by minimum severity.
+	 * `minSeverity` includes only diagnostics with severity ≤ the given value
+	 * (1=Error, 2=Warning, 3=Info, 4=Hint). Omit to include all.
+	 */
+	formatFiltered(uri: string, minSeverity?: number): string {
+		let diags = this.getMerged(uri);
+		if (minSeverity !== undefined) {
+			diags = diags.filter((d) => (d.severity ?? 0) <= minSeverity);
+		}
 		if (diags.length === 0) return "";
 		const lines: string[] = [];
 		for (const d of diags) {
@@ -65,6 +85,10 @@ export class DiagnosticsStore {
 		}
 		return lines.join("\n");
 	}
+
+	format(uri: string): string {
+		return this.formatFiltered(uri);
+	}
 }
 
 function diagnosticKey(d: Diagnostic): string {