test: reduce and improve tests in compiler_tests.rs (section 6) (#1480)

- Remove test_pipeline_filter_compiled_output_is_valid_yaml (vacuous:
  compile+valid_yaml only); merge assert_valid_yaml into the richer
  test_pipeline_filter_has_resources_and_gate.
- Remove test_execution_context_pr_compiled_output_is_valid_yaml (same
  vacuous pattern); add assert_valid_yaml to the richer
  test_execution_context_pr_emits_prepare_step_and_prompt_supplement.
- Rewrite test_pr_filter_tier1_has_native_pr_trigger: the previous
  contains("pr:") matched pr: none (wouldn't detect a regression that
  disables the trigger), and contains("main") matched anywhere in the
  output rather than the branches include list. Replace with
  !contains("pr: none"), contains("pr:\n"), and contains("    - main").

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

tests/compiler_tests.rs

@@ -4832,17 +4832,11 @@ fn test_pr_filter_tier2_has_extension_gate() {
     assert!(compiled.contains("name: prGate"), "Should have prGate step");
 }
 
-/// Pipeline filter fixture produces valid YAML.
-#[test]
-fn test_pipeline_filter_compiled_output_is_valid_yaml() {
-    let compiled = compile_fixture("pipeline-filter-agent.md");
-    assert_valid_yaml(&compiled, "pipeline-filter-agent.md");
-}
-
-/// Pipeline filter fixture produces correct pipeline resource + gate.
+/// Pipeline filter fixture produces valid YAML and correct pipeline resource + gate.
 #[test]
 fn test_pipeline_filter_has_resources_and_gate() {
     let compiled = compile_fixture("pipeline-filter-agent.md");
+    assert_valid_yaml(&compiled, "pipeline-filter-agent.md");
 
     assert!(
         compiled.contains("pipelines:"),
@@ -5050,13 +5044,26 @@ fn test_pr_filter_synth_mode_gate_step_uses_same_job_synth_ref() {
 #[test]
 fn test_pr_filter_tier1_has_native_pr_trigger() {
     let compiled = compile_fixture("pr-filter-tier1-agent.md");
-
-    assert!(compiled.contains("pr:"), "Should have native pr: block");
+    assert_valid_yaml(&compiled, "pr-filter-tier1-agent.md");
+    // The native PR trigger block must be emitted — `pr: none` would disable it.
+    assert!(
+        !compiled.contains("pr: none"),
+        "Should not disable PR trigger — fixture has native pr branches filter"
+    );
+    assert!(
+        compiled.contains("pr:\n"),
+        "Should have native pr: block (not `pr: none`)"
+    );
     assert!(
         compiled.contains("branches:"),
         "Should have branches filter"
     );
-    assert!(compiled.contains("main"), "Should include main branch");
+    // "main" must appear as an indented list item inside the branches block,
+    // not just anywhere in the compiled output (comments, other fields, etc.).
+    assert!(
+        compiled.contains("    - main"),
+        "Should include main as an indented list item in the branches include block"
+    );
 }
 
 /// Extension gate steps are correctly nested inside the Setup job's steps: block.
@@ -5951,15 +5958,6 @@ fn test_job_target_with_setup_emits_dual_branch_dependson_with_each() {
 // Execution-context extension (issue #860)
 // ============================================================================
 
-/// The execution-context extension is always-on and emits an `aw-context`
-/// prepare step on PR-triggered agents. This sanity check makes sure the
-/// generated YAML round-trips through `serde_yaml`.
-#[test]
-fn test_execution_context_pr_compiled_output_is_valid_yaml() {
-    let compiled = compile_fixture("execution-context-agent.md");
-    assert_valid_yaml(&compiled, "execution-context-agent.md");
-}
-
 /// Spot-checks the key components of the precompute step. v7 ports
 /// the precompute logic to an `ado-script` bundle
 /// (`exec-context-pr.js`), so the bash step is now a slim node
@@ -5971,6 +5969,7 @@ fn test_execution_context_pr_compiled_output_is_valid_yaml() {
 #[test]
 fn test_execution_context_pr_emits_prepare_step_and_prompt_supplement() {
     let compiled = compile_fixture("execution-context-agent.md");
+    assert_valid_yaml(&compiled, "execution-context-agent.md");
 
     assert!(
         compiled.contains("Stage PR execution context (aw-context/pr/*)"),