feat(server): workspace_panes envelope + read_tab_by_number tool

Widen the sessions.workspace_panes JSONB from a bare WorkspacePane[] to a
WorkspaceState envelope { panes, tabNumbers, nextTabNumber, closedPaneStack }.
The PATCH validator accepts either the legacy array or the envelope (zod union)
and normalizes to a full envelope before storing, so existing array-shaped rows
migrate transparently on next write. The session_workspace_updated WS frame
schema is widened to match (kept byte-identical to the web copy; parity test
passes).

Adds read_tab_by_number, a read-only tool that resolves a session-scoped tab
number to its chat via the persisted tabNumbers map and returns that chat's
transcript (oldest-first, sentinels skipped, capped at 20k chars). Tools gain an
optional ToolExecCtx ({ sql, sessionId }) 4th param on ToolDef.execute, threaded
through executeToolCall from executeToolPhase; the param is optional so existing
filesystem tools and the apps/coder consumer stay compatible. Registered in
ALL_TOOLS + READ_ONLY_TOOL_NAMES.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/services/inference/tool-phase.ts

@@ -2,6 +2,7 @@ import type { Agent, Session, ToolCall } from '../../types/api.js';
 import * as modelContext from '../model-context.js';
 import { PathScopeError } from '../path_guard.js';
 import { TOOLS_BY_NAME } from '../tools.js';
+import type { ToolExecCtx } from '../tools.js';
 import { matchToolGlob } from '../agents.js';
 import { maybeFlagForCompaction } from './payload.js';
 import { insertParts, partsFromAssistantMessage, partsFromToolMessage } from './parts.js';
@@ -31,6 +32,7 @@ async function executeToolCall(
   projectRoot: string,
   toolCall: ToolCall,
   extraRoots: readonly string[],
+  toolCtx?: ToolExecCtx,
 ): Promise<{ output: unknown; truncated: boolean; error?: string }> {
   const tool = TOOLS_BY_NAME[toolCall.name];
   if (!tool) {
@@ -65,7 +67,7 @@ async function executeToolCall(
     };
   }
   try {
-    const output = await tool.execute(parsed.data, projectRoot, extraRoots);
+    const output = await tool.execute(parsed.data, projectRoot, extraRoots, toolCtx);
     const truncated =
       typeof output === 'object' && output !== null && 'truncated' in output
         ? Boolean((output as { truncated: unknown }).truncated)
@@ -289,7 +291,10 @@ export async function executeToolPhase(
         });
         return;
       }
-      const tres = await executeToolCall(projectRoot, tc, session.allowed_read_paths);
+      const tres = await executeToolCall(projectRoot, tc, session.allowed_read_paths, {
+        sql: ctx.sql,
+        sessionId,
+      });
       if (SYNTHESIS_TOOLS.has(tc.name)) {
         synthEntries.push({ tc, output: tres.output, ...(tres.error ? { error: tres.error } : {}) });
       }