Fix: expandPrompt scanner now ignores vars inside fenced code blocks (#45)

dev/state/task-ledger.json

@@ -0,0 +1,56 @@
+{
+  "T01_GUARD_CHECK": {
+    "status": "done",
+    "evidence": [
+      "gh pr view 46 --json state,mergedAt -q '.state' => OPEN",
+      "PR is OPEN — proceeding with analysis"
+    ],
+    "last_verified": "2026-06-23T00:00:00Z"
+  },
+  "T02_RCA_5WHY": {
+    "status": "done",
+    "evidence": [
+      "WHY1: Harness crashes with 'unbound variable' because render.py emits set -euo pipefail (line 26) and references a var that is never defined in harness scope.",
+      "WHY2: CURRENT_BRANCH is referenced in the harness because re.findall over step.prompt collected it from inside the fenced code block.",
+      "WHY3: Scanner picked up fenced-block vars because re.findall treated prompt as flat text with no markdown awareness.",
+      "WHY4: No markdown awareness because expandPrompt was designed only for harness-level params (${ISSUE_NUMBER}) and did not anticipate prompts embedding shell snippets as LLM instructions.",
+      "WHY5: Edge case not anticipated because original design assumed every $VAR in a prompt was a harness parameter; no test coverage for mixed prompts with code fences.",
+      "ROOT CAUSE: _render_step_body expandPrompt scanner was context-free — no distinction between text regions and fenced code regions."
+    ],
+    "last_verified": "2026-06-23T00:01:00Z"
+  },
+  "T03_PLAN_FIX": {
+    "status": "done",
+    "evidence": [
+      "Plan: Strip fenced code blocks from step.prompt before scanning for variables.",
+      "Use re.sub(r'```.*?```', '', step.prompt, flags=re.DOTALL) to produce _prompt_no_code.",
+      "Run both braced and bare re.findall against _prompt_no_code.",
+      "Add tests: braced vars in fences NOT expanded, bare vars in fences NOT expanded, vars outside fences still expanded.",
+      "PR #46 implementation matches plan exactly per diff: render.py +3/-2, tests +59/-0.",
+      "gh pr view 46 --json mergeable,mergeStateStatus => {mergeable:MERGEABLE, mergeStateStatus:CLEAN}"
+    ],
+    "last_verified": "2026-06-23T00:02:00Z"
+  },
+  "T04_IMPLEMENT": {
+    "status": "done",
+    "evidence": [
+      "Implementation already present at HEAD commit 4840ee1 on branch fix/issue-45-expand-prompt-fenced-code-blocks",
+      "render.py:329: _prompt_no_code = re.sub(r'```.*?```', '', step.prompt, flags=re.DOTALL)",
+      "render.py:330-331: braced and bare findall run against _prompt_no_code",
+      "tests/test_workflow_to_harness.py: 2 new tests added — test_render_harness_expand_prompt_ignores_braced_vars_inside_fenced_code_blocks and test_render_harness_expand_prompt_ignores_bare_vars_inside_fenced_code_blocks",
+      "uv run --locked pytest => 111 passed in 21.51s",
+      "make qa => QA passed (ruff check, ruff format, py_compile, pytest, uv build all green)"
+    ],
+    "last_verified": "2026-06-23T00:03:00Z"
+  },
+  "T05_COMMIT_PUSH": {
+    "status": "in_progress",
+    "evidence": [],
+    "last_verified": ""
+  },
+  "T06_CI_OBSERVE": {
+    "status": "pending",
+    "evidence": [],
+    "last_verified": ""
+  }
+}

src/flowsh_cli/render.py

@@ -326,8 +326,9 @@ def _render_step_body(step: Step) -> list[str]:
             ]
         )
         if step.expandPrompt:
-            braced = re.findall(r"\$\{([A-Z_][A-Z0-9_]*)\}", step.prompt)
-            bare = re.findall(r"\$([A-Z_][A-Z0-9_]*)(?!\w)", step.prompt)
+            _prompt_no_code = re.sub(r"```.*?```", "", step.prompt, flags=re.DOTALL)
+            braced = re.findall(r"\$\{([A-Z_][A-Z0-9_]*)\}", _prompt_no_code)
+            bare = re.findall(r"\$([A-Z_][A-Z0-9_]*)(?!\w)", _prompt_no_code)
             seen: dict[str, None] = {}
             for var in braced + bare:
                 seen[var] = None

tests/test_workflow_to_harness.py

@@ -591,6 +591,65 @@ def test_render_harness_safe_variable_substitution_when_expand_prompt_enabled()
     assert '_p=\'$ISSUE_NUMBER\'; prompt="${prompt//"$_p"/"$ISSUE_NUMBER"}"' in script
 
 
+def test_render_harness_expand_prompt_ignores_braced_vars_inside_fenced_code_blocks() -> None:
+    workflow = Workflow(
+        id="wf_prompt_expand_code_fence",
+        name="Prompt Expand Code Fence",
+        steps=[
+            AgentStep(
+                type="agent",
+                prompt=(
+                    "Work on issue ${ISSUE_NUMBER}.\n"
+                    "\n"
+                    "Check for an existing PR:\n"
+                    "\n"
+                    "```bash\n"
+                    "CURRENT_BRANCH=$(git branch --show-current)\n"
+                    'EXISTING_PR=$(gh pr list --head "$CURRENT_BRANCH")\n'
+                    "```\n"
+                    "\n"
+                    "If [EXISTING_PR] is set, skip PR creation."
+                ),
+                expandPrompt=True,
+            )
+        ],
+    )
+
+    script = render_harness(workflow)
+
+    # ISSUE_NUMBER appears outside the code block — must still be expanded
+    assert '_p=\'${ISSUE_NUMBER}\'; prompt="${prompt//"$_p"/"$ISSUE_NUMBER"}"' in script
+    assert '_p=\'$ISSUE_NUMBER\'; prompt="${prompt//"$_p"/"$ISSUE_NUMBER"}"' in script
+    # CURRENT_BRANCH and EXISTING_PR are inside the code block — must NOT be expanded
+    assert "_p='${CURRENT_BRANCH}'" not in script
+    assert "_p='$CURRENT_BRANCH'" not in script
+    assert "_p='${EXISTING_PR}'" not in script
+    assert "_p='$EXISTING_PR'" not in script
+
+
+def test_render_harness_expand_prompt_ignores_bare_vars_inside_fenced_code_blocks() -> None:
+    workflow = Workflow(
+        id="wf_prompt_expand_bare_code_fence",
+        name="Prompt Expand Bare Code Fence",
+        steps=[
+            AgentStep(
+                type="agent",
+                prompt=("Run the build for $TARGET_ENV.\n\n```bash\n./build.sh $BUILD_FLAGS\n```"),
+                expandPrompt=True,
+            )
+        ],
+    )
+
+    script = render_harness(workflow)
+
+    # TARGET_ENV is outside the code block — must be expanded
+    assert '_p=\'${TARGET_ENV}\'; prompt="${prompt//"$_p"/"$TARGET_ENV"}"' in script
+    assert '_p=\'$TARGET_ENV\'; prompt="${prompt//"$_p"/"$TARGET_ENV"}"' in script
+    # BUILD_FLAGS is inside the code block — must NOT be expanded
+    assert "_p='${BUILD_FLAGS}'" not in script
+    assert "_p='$BUILD_FLAGS'" not in script
+
+
 def test_render_harness_disambiguates_duplicate_step_function_names(tmp_path: Path) -> None:
     workflow_file = tmp_path / "workflows.yml"
     workflow_file.write_text(