Add agent import smoke test and [agents]-extra test job to PR CI

Extends the existing single unit-test job (rather than adding a new
job) to match its established pattern: per-step continue-on-error +
a final aggregating "Check test results" gate.

- "Verify agents import without extras installed" runs right after the
  existing base `pip install -e .` step (already extras-free) and
  before any agents-specific install, so it genuinely exercises the
  no-extras case -- this is the regression class the Stage 1 langchain.py
  fix addressed.
- "Install agents extra" + "Run agent tests" run after the three
  existing suites, installing `.[agents]` plus pytest-asyncio.
  pytest-asyncio is required explicitly here: it's declared in
  [tool.poetry.group.dev.dependencies], but this workflow installs via
  plain pip (not `poetry install`), which never sees poetry dependency
  groups -- confirmed by simulating the exact CI command sequence in a
  fresh venv, which reproduced 30 async-test failures
  ("async def functions are not natively supported") until
  pytest-asyncio was installed explicitly. pytest-xdist and
  pytest-rerunfailures (also dev-group-only) are not added since
  nothing in tests/ai depends on either.
- Both new steps feed the existing coverage-file-per-suite +
  `coverage combine` pattern automatically (the combine step already
  globs `.coverage.*`), and both are added to the final
  "Check test results" gate.

Verified by replicating this exact install/test sequence end-to-end in
a throwaway venv: base install + smoke test, all three existing suites,
agents-extra install, agent suite, coverage combine across all 4 files
-- all green (1683 agent tests passed, existing suites unaffected).

e2e/ is intentionally not wired in here (still-open item: what server
these hit once Agentspan's own is discarded).

Author: Kowser

.github/workflows/pull_request.yml

@@ -27,6 +27,12 @@ jobs:
           pip install -e .
           pip install pytest pytest-cov coverage
 
+      - name: Verify agents import without extras installed
+        id: agent_base_import
+        continue-on-error: true
+        run: |
+          python -c "import conductor.ai.agents"
+
       - name: Prepare coverage directory
         run: |
           mkdir -p ${{ env.COVERAGE_DIR }}
@@ -64,6 +70,19 @@ jobs:
         run: |
           coverage run -m pytest tests/serdesertest -v
 
+      - name: Install agents extra
+        run: |
+          pip install -e '.[agents]'
+          pip install pytest-asyncio
+
+      - name: Run agent tests
+        id: agent_tests
+        continue-on-error: true
+        env:
+          COVERAGE_FILE: ${{ env.COVERAGE_DIR }}/.coverage.agents
+        run: |
+          coverage run -m pytest tests/ai -m "not integration and not e2e" -v
+
       - name: Generate coverage report
         id: coverage_report
         run: |
@@ -91,5 +110,5 @@ jobs:
           file: coverage.xml
 
       - name: Check test results
-        if: steps.unit_tests.outcome == 'failure' || steps.bc_tests.outcome == 'failure' || steps.serdeser_tests.outcome == 'failure'
+        if: steps.unit_tests.outcome == 'failure' || steps.bc_tests.outcome == 'failure' || steps.serdeser_tests.outcome == 'failure' || steps.agent_base_import.outcome == 'failure' || steps.agent_tests.outcome == 'failure'
         run: exit 1