You are a senior code reviewer preparing to review code changes.

## Code Changes

```diff
diff --git a/ftl_code_expert/cli.py b/ftl_code_expert/cli.py
index 4dfa992..7a632b5 100644
--- a/ftl_code_expert/cli.py
+++ b/ftl_code_expert/cli.py
@@ -1323,51 +1323,71 @@ def walk_commits(ctx, since, since_commit, since_last, dry_run):
         return
 
     # Retract beliefs sourced from deleted files
     if deleted_files:
         _retract_beliefs_for_deleted_files(deleted_files)
 
     if not check_model_available(model):
         click.echo(f"Error: Model '{model}' CLI not available", err=True)
         sys.exit(1)
 
-    # Explore each unique file
-    explored = 0
-    skipped = 0
+    # Build topics for each unique file
     from .topics import Topic
+    timeout = ctx.obj["timeout"]
+    parallel = ctx.obj["parallel"]
+    topics_with_commits = []
+    skipped = 0
     for file_path, commit in file_to_commit.items():
-        explored += 1
-        click.echo(f"\n{'=' * 40}", err=True)
-        click.echo(
-            f"[{explored}/{total_files}] {file_path} (from {commit['sha'][:8]})",
-            err=True,
-        )
-        click.echo(f"{'=' * 40}", err=True)
+        abs_path = os.path.join(abs_repo, file_path)
+        if not os.path.isfile(abs_path):
+            click.echo(f"  File not found (deleted?): {file_path}, skipping", err=True)
+            skipped += 1
+            continue
 
         topic = Topic(
             title=f"{commit['subject']} — {file_path}",
             kind="file",
             target=file_path,
             source=f"walk-commits:{commit['sha'][:8]}",
         )
+        topics_with_commits.append((topic, commit))
 
-        abs_path = os.path.join(abs_repo, file_path)
-        if not os.path.isfile(abs_path):
-            click.echo(f"  File not found (deleted?): {file_path}, skipping", err=True)
-            skipped += 1
-            continue
+    # Explore in batches
+    explored = 0
+    all_topics = [t for t, _ in topics_with_commits]
+    while explored < len(all_topics):
+        batch = all_topics[explored:explored + parallel]
+        click.echo(f"\n{'=' * 40}", err=True)
+        click.echo(f"[{explored + 1}-{explored + len(batch)}/{len(all_topics)}]", err=True)
+        click.echo(f"{'=' * 40}", err=True)
+        for topic in batch:
+            click.echo(f"  [{topic.kind}] {topic.target}", err=True)
 
-        _run_file_topic(ctx, topic, model, abs_repo)
+        if parallel > 1 and len(batch) > 1:
+            results = asyncio.run(
+                _explore_topics_concurrent(batch, model, abs_repo, timeout, parallel)
+            )
+            for r in results:
+                if isinstance(r, Exception):
+                    click.echo(f"  Error: {r}", err=True)
+                elif r is not None:
+                    _, result, entry_name, entry_title, source = r
+                    _finalize_topic(ctx, entry_name, entry_title, source, result)
+        else:
+            for topic in batch:
+                _run_file_topic(ctx, topic, model, abs_repo)
+
+        explored += len(batch)
 
     # Save checkpoint so --since-last works next time
     save_diff_checkpoint(project_dir, cwd=abs_repo)
-    click.echo(f"\nWalked {len(commits)} commit(s), explored {explored - skipped} file(s) ({skipped} skipped)", err=True)
+    click.echo(f"\nWalked {len(commits)} commit(s), explored {len(all_topics)} file(s) ({skipped} skipped)", err=True)
     click.echo("Diff checkpoint saved.", err=True)
 
 
 # --- propose-beliefs ---
 
 
 @cli.command("propose-beliefs")
 @click.option("--batch-size", type=int, default=5, help="Entries per LLM batch (default: 5)")
 @click.option("--output", default="proposed-beliefs.md", help="Output file")
 @click.option("--model", "-m", default=None, help="Override model")

```

## Your Task

Analyze the diff and identify what additional information you need to render confident verdicts.
Do NOT render verdicts yet. Only request observations.

## Available Observation Tools

| Tool | Purpose | When to use |
|------|---------|-------------|
| `exception_hierarchy` | Show exception MRO and subclasses | Retry logic, exception handling |
| `raises_analysis` | What exceptions a function raises | New function calls, error paths |
| `call_graph` | What a function calls | Impact analysis |
| `find_usages` | Where a symbol is used (with prod/test split) | Quick integration lookup |
| `find_callers` | Caller analysis with prod/test split and calling context | Method signature changes, return type changes, constructor modifications, integration verification |
| `test_coverage` | Find tests for a file (uses coverage-map if available) | Test coverage claims |
| `coverage_map_tests` | Find tests covering a file (from coverage-map.json) | Precise test coverage from actual execution |
| `coverage_map_files` | Find files covered by tests matching a pattern | Impact analysis for test changes |
| `function_body` | Full source of a function/method | Need complete function context beyond diff hunks |
| `file_imports` | Extract imports from a file | Verify import changes, check dependencies |
| `project_dependencies` | Get pyproject.toml/requirements.txt | Verify new imports have dependencies |
| `related_test_files` | Find test files for a source file | Discover tests by naming, imports, and coverage map |
| `class_hierarchy` | Show base classes and their `__init__` signatures | Class changes its parent, modifies `__init__`, or uses `super()` |
| `symbol_migration` | Check if a rename is complete across the repo | Symbol renamed in diff — verify old name is fully removed |
| `generator_info` | Report whether a function uses `yield` | Function might be a generator — affects return value semantics |

## What to Look For

1. **Exception handling**: Any `retry_if_exception_type`, `except`, or exception class references
2. **New dependencies**: Calls to external libraries where you don't know the error behavior
3. **Behavioral changes**: Modified logic where you need to verify callers/callees
4. **Test claims**: References to tests you can't see in the diff
5. **Inheritance changes**: Class definition changes, new base classes, `super()` calls
6. **Renames**: Symbols that appear to have been renamed in the diff
7. **Factory methods**: Calls to `@classmethod` / `@staticmethod` constructors (e.g. `Result.error(...)`) — request `function_body` to see their implementation

## Output Format

Output a JSON array of observation requests:

```json
[
  {"name": "descriptive_name", "tool": "tool_name", "params": {"param": "value"}},
  ...
]
```

If you don't need any observations (simple changes, all context is in the diff), output:

```json
[]
```

## Examples

For a diff containing `retry_if_exception_type((OSError, httpx.TransportError))`:
```json
[
  {"name": "oserror_subclasses", "tool": "exception_hierarchy", "params": {"class_name": "builtins.OSError"}},
  {"name": "transport_errors", "tool": "exception_hierarchy", "params": {"class_name": "httpx.TransportError"}}
]
```

For a diff adding a new function that calls `oauth_client.get_access_token()`:
```json
[
  {"name": "oauth_exceptions", "tool": "raises_analysis", "params": {"file_path": "src/auth/oauth.py", "function_name": "get_access_token"}}
]
```

For a diff modifying a method but you need the full function to verify:
```json
[
  {"name": "full_getattr", "tool": "function_body", "params": {"file_path": "src/proxy.py", "function_name": "__getattr__"}}
]
```

For a diff changing a method signature or return type (verify all callers):
```json
[
  {"name": "handle_request_callers", "tool": "find_callers", "params": {"symbol": "handle_request"}}
]
```

For a diff adding new imports (e.g., `import httpx`):
```json
[
  {"name": "file_imports", "tool": "file_imports", "params": {"file_path": "src/client.py"}},
  {"name": "project_deps", "tool": "project_dependencies", "params": {}}
]
```

For a diff calling a factory method like `ModuleResult.error_result(msg)`:
```json
[
  {"name": "error_result_body", "tool": "function_body", "params": {"file_path": "src/models.py", "function_name": "error_result"}}
]
```

For a diff where a class changes its parent class:
```json
[
  {"name": "client_hierarchy", "tool": "class_hierarchy", "params": {"class_name": "MyClient", "file_path": "src/client.py"}}
]
```

For a diff that renames a symbol (e.g., `OldClient` to `NewClient`):
```json
[
  {"name": "client_rename", "tool": "symbol_migration", "params": {"old_name": "OldClient", "new_name": "NewClient"}}
]
```

For a diff modifying a function that might be a generator:
```json
[
  {"name": "process_gen", "tool": "generator_info", "params": {"file_path": "src/pipeline.py", "function_name": "process_items"}}
]
```

Now analyze the diff above and output your observation requests as JSON:
