fix(aimock): validate fixtures at load time to prevent runtime 500s (CopilotKit#3973)

## Summary

Follow-up hardening to CopilotKit#3971. aimock supports fixture schema validation
at startup via `--validate-on-load`, but the flag is **opt-in** and the
showcase Dockerfile was not passing it. That meant fixtures with
unrecognized response keys (e.g. `"text"` instead of `"content"`) loaded
silently and only surfaced as HTTP 500s at request time — which is
exactly what crashed crewai-crews and triggered CopilotKit#3971.

This PR wires up two independent safety nets so a broken fixture can't
ship again:

1. **Dockerfile (fail-fast at container boot)** —
`showcase/aimock/Dockerfile` now passes `--validate-on-load`. If any
fixture fails the aimock schema, the container exits non-zero instead of
starting and serving 500s. Railway will not promote a bad build.
2. **CI test (fail-fast in PR review)** — new vitest spec at
`showcase/scripts/__tests__/aimock-fixtures.test.ts` imports
`loadFixtureFile` + `validateFixtures` from `@copilotkit/aimock` and
asserts zero errors against both `feature-parity.json` and `smoke.json`.
Runs inside the existing ` Showcase: Validate` workflow
(`showcase/scripts` vitest suite) on every PR that touches
`showcase/**`.

## Verification

**Red-green on the vitest spec:**
- Rebased onto the tip of main *before* CopilotKit#3971 merged: the spec fails
with 5 errors — exactly the 5 broken `"text"` fixtures (`plan`, `steps`,
`mars`, `dashboard`, `report`) that CopilotKit#3971 repaired.
- Rebased forward onto main *after* CopilotKit#3971: spec passes with 0 errors,
all 549 showcase/scripts tests green.

**Red-green on the Dockerfile:**
- Current fixtures + `--validate-on-load`: container boots cleanly, logs
`Loaded 39 fixture(s) from /fixtures`.
- Injecting an intentionally broken fixture (`response: { "text": "..."
}`): container fails to start with `[aimock] Fixture 0: response is not
a recognized type (must have content, toolCalls, error, or embedding)` /
`Validation failed: 1 error(s), 0 warning(s)` and non-zero exit.

## Test plan

- [x] Local: full `showcase/scripts` vitest suite passes (549/549)
- [x] Local: `pnpm run test` (monorepo) passes
- [x] Docker: image builds and starts with `--validate-on-load` against
current fixtures
- [x] Docker red-green: broken fixture fails container start with
non-zero exit
- [ ] CI: ` Showcase: Validate` job runs the new test file on PR

Author: jpr5

.github/workflows/showcase_aimock-e2e.yml

@@ -78,7 +78,7 @@ jobs:
       - name: Start aimock
         run: |
           npm install -g @copilotkit/aimock@latest
-          npx aimock --port 4010 --host 127.0.0.1 --fixtures showcase/aimock/feature-parity.json &
+          npx aimock --port 4010 --host 127.0.0.1 --fixtures showcase/aimock/feature-parity.json --validate-on-load &
           # Wait for aimock to be ready
           for i in $(seq 1 20); do
             curl -sf http://localhost:4010/ > /dev/null 2>&1 && break

.github/workflows/showcase_validate.yml

@@ -4,10 +4,14 @@ on:
   pull_request:
     paths:
       - "showcase/**"
+      - "examples/integrations/**/fixtures/**"
+      - "scripts/doc-tests/fixtures/**"
   push:
     branches: [main]
     paths:
       - "showcase/**"
+      - "examples/integrations/**/fixtures/**"
+      - "scripts/doc-tests/fixtures/**"
 
 concurrency:
   group: showcase-validate-${{ github.ref }}

.github/workflows/test_doc-examples.yml

@@ -42,7 +42,7 @@ jobs:
           echo "aimock binary: $AIMOCK_BIN"
           ls -la "$AIMOCK_BIN" || echo "binary not found at expected path"
           which aimock || echo "aimock not on PATH"
-          nohup node $(npm root -g)/@copilotkit/aimock/dist/cli.js --fixtures scripts/doc-tests/fixtures > /tmp/aimock.log 2>&1 &
+          nohup node $(npm root -g)/@copilotkit/aimock/dist/cli.js --fixtures scripts/doc-tests/fixtures --validate-on-load > /tmp/aimock.log 2>&1 &
           for i in $(seq 1 60); do
             if curl -sf http://localhost:4010/health; then
               echo "aimock ready"

examples/integrations/adk/docker-compose.test.yml

@@ -3,7 +3,8 @@ services:
     image: ghcr.io/copilotkit/aimock:latest
     volumes:
       - ./fixtures:/fixtures:ro
-    command: ["--fixtures", "/fixtures", "--host", "0.0.0.0"]
+    command:
+      ["--fixtures", "/fixtures", "--host", "0.0.0.0", "--validate-on-load"]
 
   agent:
     build:

examples/integrations/agno/docker-compose.test.yml

@@ -3,7 +3,8 @@ services:
     image: ghcr.io/copilotkit/aimock:latest
     volumes:
       - ./fixtures:/fixtures:ro
-    command: ["--fixtures", "/fixtures", "--host", "0.0.0.0"]
+    command:
+      ["--fixtures", "/fixtures", "--host", "0.0.0.0", "--validate-on-load"]
 
   agent:
     build:

examples/integrations/crewai-crews/docker-compose.test.yml

@@ -3,7 +3,8 @@ services:
     image: ghcr.io/copilotkit/aimock:latest
     volumes:
       - ./fixtures:/fixtures:ro
-    command: ["--fixtures", "/fixtures", "--host", "0.0.0.0"]
+    command:
+      ["--fixtures", "/fixtures", "--host", "0.0.0.0", "--validate-on-load"]
 
   agent:
     build:

examples/integrations/langgraph-fastapi/docker-compose.test.yml

@@ -6,7 +6,8 @@ services:
     image: ghcr.io/copilotkit/aimock:latest
     volumes:
       - ./fixtures:/fixtures:ro
-    command: ["--fixtures", "/fixtures", "--host", "0.0.0.0"]
+    command:
+      ["--fixtures", "/fixtures", "--host", "0.0.0.0", "--validate-on-load"]
 
   agent:
     build:

examples/integrations/langgraph-js/docker-compose.test.yml

@@ -6,7 +6,8 @@ services:
     image: ghcr.io/copilotkit/aimock:latest
     volumes:
       - ./fixtures:/fixtures:ro
-    command: ["--fixtures", "/fixtures", "--host", "0.0.0.0"]
+    command:
+      ["--fixtures", "/fixtures", "--host", "0.0.0.0", "--validate-on-load"]
 
   agent:
     build:

examples/integrations/langgraph-python-threads/docker-compose.test.yml

@@ -6,7 +6,8 @@ services:
     image: ghcr.io/copilotkit/aimock:latest
     volumes:
       - ./fixtures:/fixtures:ro
-    command: ["--fixtures", "/fixtures", "--host", "0.0.0.0"]
+    command:
+      ["--fixtures", "/fixtures", "--host", "0.0.0.0", "--validate-on-load"]
 
   agent:
     build:

examples/integrations/langgraph-python/docker-compose.test.yml

@@ -6,7 +6,8 @@ services:
     image: ghcr.io/copilotkit/aimock:latest
     volumes:
       - ./fixtures:/fixtures:ro
-    command: ["--fixtures", "/fixtures", "--host", "0.0.0.0"]
+    command:
+      ["--fixtures", "/fixtures", "--host", "0.0.0.0", "--validate-on-load"]
 
   agent:
     build: