fix(generator): render typed Parameters/Returns columns without polish (#30)

[silversurfer562]

Summary

• Fixes Regeneration silently drops parameter/return columns and frontmatter when polish is bypassed #30: regeneration of .help/templates/<feature>/reference.md silently drops the Parameters and Returns columns + human description when the LLM polish pass is bypassed.
• Threads typed argument and return data from the AST through the Jinja template so the 4-column table renders without depending on polish.
• Polish keeps its job (rewriting prose) but is no longer load-bearing for structural columns.

What changed

• _collect_function now also stores params: str and returns: str on each function_signatures entry, computed from the existing formatted signature via a small _split_signature helper. No new AST traversal.
• _render_template (the .help/ path) now passes function_signatures and class_signatures into the Jinja render call alongside the legacy public_functions / public_classes.
• meta_templates/reference.md.j2:
  • Renders feature.description directly under the title, so the intro from features.yaml survives without polish.
  • Renders a Function | Parameters | Returns | Description | File table from function_signatures when available, falling back to the previous 3-column shape from public_functions when only the legacy data is present.

Why

A regression slipped into attune-rag's main branch this week — see attune-rag d39e39d. Regenerating .help/templates/benchmark/reference.md with polish bypassed dropped Parameters / Returns columns and the human description. The diff looked normal at review time (frontmatter + headings + a function table) so it merged.

The data the user lost was already present on _SourceInfo.function_signatures from the AST — it just wasn't being threaded into the Jinja render call.

Before / after

Before (raw Jinja, polish bypassed):

```markdown

Benchmark reference

Functions

Function	Description	File
`main()`	—	`src/attune_rag/benchmark.py`
```

After (raw Jinja, polish still bypassed):

```markdown

Benchmark reference

Precision/recall/faithfulness benchmark runner — gates CI on configurable thresholds; supports custom query files and optional faithfulness scoring via --with-faithfulness

Functions

Function	Parameters	Returns	Description	File
`main`	`argv: list[str] | None = None`	`int`	Run benchmark suite and return exit code	`src/attune_rag/benchmark.py`
```

Test plan

• New TestSplitSignature unit tests: typed params + return, no-return, complex pipe-union return, defensive no-match shape.
• New TestReferenceTemplateColumns asserts the rendered reference template contains the 4-column header, typed parameters, return annotation, and the feature description — without polish.
• Updated reference golden snapshot reflects the new shape.
• Dogfood help tests (tests/test_dogfood_help.py) still pass.
• Polish-cache-isolated full run: only one pre-existing failure (test_task_template_matches_snapshot — cache cross-contamination with a real API key in .env, reproducible on main, unrelated to this change).

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