feat: MCP {env:VAR} key substitution + coder model/tool-result fixes + docs refactor (v2.7.9)

- MCP secrets: substituteEnvVars recursively resolves {env:NAME} in mcp.json string values from process.env before Zod (opencode-compatible); unset -> '' + boot warning, and invalid-config log names the unset vars (an empty {env:VAR} in a strict url/command field invalidates the whole config)
- data/mcp.json now untracked (.gitignore flips !data/mcp.json -> !data/mcp.example.json); tracked template data/mcp.example.json carries "{env:CONTEXT7_API_KEY}"; .env.example documents the key (9 mcp-config tests)
- Coder fix: message_complete frame model widened string -> string|null (server+web ws-frames parity); dispatcher publishes model: task.model at all 4 external completion points — a null model otherwise fail-closed in publishFrame and dropped the whole frame incl. status:'complete' (regression test)
- Coder fix: claude-sdk mapUserToolResults maps user-message tool_result blocks -> terminal tool_update events (completed/failed w/ output) so tool snapshots resolve instead of spinning forever
- Composer: AgentComposerBar drops §9b resumed/history/new chip + token readout, loses flex-wrap so the row stays one line; CoderPane gains a per-chat localStorage agent-config cache (restores last model on reopen) + threads model into the timeline/chip
- Docs: root CLAUDE.md slimmed (~190 lines), per-app refs split to apps/{coder,server,web}/CLAUDE.md; new docs/coder-backends.md, docs/project-discovery.md, docs/coding-standards/ (cross-app-contract-parity); ARCHITECTURE.md links the backends doc

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

apps/server/src/services/__tests__/mcp-config.test.ts

@@ -0,0 +1,93 @@
+/**
+ * Unit tests for `{env:VAR}` substitution in the MCP config loader.
+ * Pure — no live MCP server. Verifies secrets resolve from process.env
+ * (so real keys live in `.env`, not the gitignored config file).
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { substituteEnvVars } from '../mcp-config.js';
+
+// Minimal FastifyBaseLogger stub — only .warn is exercised here.
+function fakeLog() {
+  const warnings: string[] = [];
+  const log = {
+    warn: (msg: unknown) => {
+      warnings.push(typeof msg === 'string' ? msg : JSON.stringify(msg));
+    },
+  };
+  return { log: log as never, warnings };
+}
+
+describe('substituteEnvVars', () => {
+  const SAVED = process.env.MCP_TEST_SECRET;
+  beforeEach(() => {
+    process.env.MCP_TEST_SECRET = 'resolved-value';
+  });
+  afterEach(() => {
+    if (SAVED === undefined) delete process.env.MCP_TEST_SECRET;
+    else process.env.MCP_TEST_SECRET = SAVED;
+    delete process.env.MCP_TEST_MISSING;
+  });
+
+  it('replaces a {env:VAR} reference in a string value', () => {
+    const { log } = fakeLog();
+    expect(substituteEnvVars('{env:MCP_TEST_SECRET}', log)).toBe('resolved-value');
+  });
+
+  it('substitutes inside nested objects and arrays', () => {
+    const { log } = fakeLog();
+    const out = substituteEnvVars(
+      {
+        headers: { CONTEXT7_API_KEY: '{env:MCP_TEST_SECRET}' },
+        args: ['--token', '{env:MCP_TEST_SECRET}'],
+      },
+      log,
+    );
+    expect(out).toEqual({
+      headers: { CONTEXT7_API_KEY: 'resolved-value' },
+      args: ['--token', 'resolved-value'],
+    });
+  });
+
+  it('leaves object keys untouched, only transforms values', () => {
+    const { log } = fakeLog();
+    const out = substituteEnvVars({ '{env:MCP_TEST_SECRET}': 'literal' }, log) as Record<string, string>;
+    expect(Object.keys(out)).toEqual(['{env:MCP_TEST_SECRET}']);
+  });
+
+  it('resolves an unset var to empty string and warns', () => {
+    const { log, warnings } = fakeLog();
+    expect(substituteEnvVars('{env:MCP_TEST_MISSING}', log)).toBe('');
+    expect(warnings.some((w) => w.includes('MCP_TEST_MISSING'))).toBe(true);
+  });
+
+  it('passes non-string scalars through unchanged', () => {
+    const { log } = fakeLog();
+    expect(substituteEnvVars(true, log)).toBe(true);
+    expect(substituteEnvVars(42, log)).toBe(42);
+    expect(substituteEnvVars(null, log)).toBe(null);
+  });
+
+  it('leaves strings without a reference unchanged', () => {
+    const { log } = fakeLog();
+    expect(substituteEnvVars('https://mcp.context7.com/mcp', log)).toBe('https://mcp.context7.com/mcp');
+  });
+
+  it('resolves multiple references in one string (global flag)', () => {
+    const { log } = fakeLog();
+    expect(substituteEnvVars('{env:MCP_TEST_SECRET}/{env:MCP_TEST_SECRET}', log)).toBe(
+      'resolved-value/resolved-value',
+    );
+  });
+
+  it('passes an empty string through unchanged', () => {
+    const { log } = fakeLog();
+    expect(substituteEnvVars('', log)).toBe('');
+  });
+
+  it('collects unset var names into the optional collector set', () => {
+    const { log } = fakeLog();
+    const unset = new Set<string>();
+    substituteEnvVars({ url: '{env:MCP_TEST_MISSING}', headers: { k: '{env:MCP_TEST_SECRET}' } }, log, unset);
+    expect([...unset]).toEqual(['MCP_TEST_MISSING']);
+  });
+});

apps/server/src/services/__tests__/ws-frames.test.ts

@@ -111,6 +111,19 @@ describe('WsFrameSchema (v1.13.11-a)', () => {
     expect(result.success).toBe(true);
   });
 
+  it('accepts a message_complete frame with a null model (external coder, no model selected)', () => {
+    // Regression guard: the dispatcher publishes `model: task.model` (string |
+    // null). When null, this MUST validate or publishFrame fail-closes and drops
+    // the whole frame, incl. the status:'complete' transition.
+    const result = WsFrameSchema.safeParse({
+      type: 'message_complete',
+      message_id: VALID_UUID_A,
+      chat_id: VALID_UUID_B,
+      model: null,
+    });
+    expect(result.success).toBe(true);
+  });
+
   it('every KNOWN_FRAME_TYPES entry has a discriminated branch', () => {
     // Probe each known type by attempting a minimal valid construction.
     // Failure here means the union and the KNOWN_FRAME_TYPES list drifted.