[AZ-171] Add TensorRT tests, AC coverage gate in implement skill, optimize test infrastructure

- Add TensorRT export tests with graceful skip when no GPU available
- Add AC test coverage verification step (Step 8) to implement skill
- Add test coverage gap analysis to new-task skill
- Move exported_models fixture to conftest.py as session-scoped (shared across modules)
- Reorder tests: e2e training runs first so images/labels are available for all tests
- Consolidate teardown into single session-level cleanup in conftest.py
- Fix infrastructure tests to count files dynamically instead of hardcoded 20

Made-with: Cursor

.cursor/skills/implement/SKILL.md

@@ -94,6 +94,7 @@ For each task in the batch, launch an `implementer` subagent with:
 - List of files OWNED (exclusive write access)
 - List of files READ-ONLY
 - List of files FORBIDDEN
+- **Explicit instruction**: the implementer must write or update tests that validate each acceptance criterion in the task spec. If a test cannot run in the current environment (e.g., TensorRT requires GPU), the test must still be written and skip with a clear reason.
 
 Launch all subagents immediately — no user confirmation.
 
@@ -108,46 +109,64 @@ Launch all subagents immediately — no user confirmation.
 - Subagent has not produced new output for an extended period → flag as potentially hung
 - If a subagent is flagged as stuck, do NOT let it continue looping — stop it and record the blocker in the batch report
 
-### 8. Code Review
+### 8. AC Test Coverage Verification
+
+Before code review, verify that every acceptance criterion in each task spec has at least one test that validates it. For each task in the batch:
+
+1. Read the task spec's **Acceptance Criteria** section
+2. Search the test files (new and existing) for tests that cover each AC
+3. Classify each AC as:
+   - **Covered**: a test directly validates this AC (running or skipped-with-reason)
+   - **Not covered**: no test exists for this AC
+
+If any AC is **Not covered**:
+- This is a **BLOCKING** failure — the implementer must write the missing test before proceeding
+- Re-launch the implementer with the specific ACs that need tests
+- If the test cannot run in the current environment (GPU required, platform-specific, external service), the test must still exist and skip with `pytest.mark.skipif` or `pytest.skip()` explaining the prerequisite
+- A skipped test counts as **Covered** — the test exists and will run when the environment allows
+
+Only proceed to Step 9 when every AC has a corresponding test.
+
+### 9. Code Review
 
 - Run `/code-review` skill on the batch's changed files + corresponding task specs
 - The code-review skill produces a verdict: PASS, PASS_WITH_WARNINGS, or FAIL
 
-### 9. Auto-Fix Gate
+### 10. Auto-Fix Gate
 
 Auto-fix loop with bounded retries (max 2 attempts) before escalating to user:
 
-1. If verdict is **PASS** or **PASS_WITH_WARNINGS**: show findings as info, continue automatically to step 10
+1. If verdict is **PASS** or **PASS_WITH_WARNINGS**: show findings as info, continue automatically to step 11
 2. If verdict is **FAIL** (attempt 1 or 2):
    - Parse the code review findings (Critical and High severity items)
    - For each finding, attempt an automated fix using the finding's location, description, and suggestion
    - Re-run `/code-review` on the modified files
-   - If now PASS or PASS_WITH_WARNINGS → continue to step 10
+   - If now PASS or PASS_WITH_WARNINGS → continue to step 11
    - If still FAIL → increment retry counter, repeat from (2) up to max 2 attempts
 3. If still **FAIL** after 2 auto-fix attempts: present all findings to user (**BLOCKING**). User must confirm fixes or accept before proceeding.
 
 Track `auto_fix_attempts` count in the batch report for retrospective analysis.
 
-### 10. Commit and Push
+### 11. Commit and Push
 
 - After user confirms the batch (explicitly for FAIL, implicitly for PASS/PASS_WITH_WARNINGS):
   - `git add` all changed files from the batch
   - `git commit` with a message that includes ALL task IDs (tracker IDs or numeric prefixes) of tasks implemented in the batch, followed by a summary of what was implemented. Format: `[TASK-ID-1] [TASK-ID-2] ... Summary of changes`
   - `git push` to the remote branch
 
-### 11. Update Tracker Status → In Testing
+### 12. Update Tracker Status → In Testing
 
 After the batch is committed and pushed, transition the ticket status of each task in the batch to **In Testing** via the configured work item tracker. If `tracker: local`, skip this step.
 
-### 12. Archive Completed Tasks
+### 13. Archive Completed Tasks
 
 Move each completed task file from `TASKS_DIR/todo/` to `TASKS_DIR/done/`.
 
-### 13. Loop
+### 14. Loop
 
 - Go back to step 2 until all tasks in `todo/` are done
 
-### 14. Final Test Run
+### 15. Final Test Run
 
 - After all batches are complete, run the full test suite once
 - Read and execute `.cursor/skills/test-run/SKILL.md` (detect runner, run suite, diagnose failures, present blocking choices)
@@ -177,10 +196,11 @@ After each batch, produce a structured report:
 
 ## Task Results
 
-| Task | Status | Files Modified | Tests | Issues |
-|------|--------|---------------|-------|--------|
-| [TRACKER-ID]_[name] | Done | [count] files | [pass/fail] | [count or None] |
+| Task | Status | Files Modified | Tests | AC Coverage | Issues |
+|------|--------|---------------|-------|-------------|--------|
+| [TRACKER-ID]_[name] | Done | [count] files | [pass/fail] | [N/N ACs covered] | [count or None] |
 
+## AC Test Coverage: [All covered / X of Y covered]
 ## Code Review Verdict: [PASS/FAIL/PASS_WITH_WARNINGS]
 ## Auto-Fix Attempts: [0/1/2]
 ## Stuck Agents: [count or None]
@@ -212,4 +232,4 @@ Each batch commit serves as a rollback checkpoint. If recovery is needed:
 - Never launch tasks whose dependencies are not yet completed
 - Never allow two parallel agents to write to the same file
 - If a subagent fails or is flagged as stuck, stop it and report — do not let it loop indefinitely
-- Always run the full test suite after all batches complete (step 14)
+- Always run the full test suite after all batches complete (step 15)