fix: track() returns created Path on success (match Optional[Path] signature) - #2

Summary

MemKraft.track() declares -> Optional[Path] but the success path never returns the created Path — it falls off the end of the function and implicitly returns None. Callers that use the documented return type cannot distinguish success from failure. This PR adds the missing return filepath on success.

Problem

In src/memkraft/core.py the track() method declares:

def track(self, name: str, entity_type: str = "person", source: str = "") -> Optional[Path]:

All three failure paths return None explicitly:

But the success path ends at the print statement on line 125 and falls through, returning None implicitly — so the signature's promise of Optional[Path] is only ever a promise of None.

filepath.write_text(content, encoding="utf-8")
print(f"✅ Tracking: {filepath.relative_to(self.base_dir.parent)}")
# ← implicit None here; nothing differentiates success from failure
except OSError as e:
    ...
    return None

Fix

One line:

             filepath.write_text(content, encoding="utf-8")
             print(f"✅ Tracking: {filepath.relative_to(self.base_dir.parent)}")
+            return filepath
         except OSError as e:

Why it matters

• Library users who want the created path currently have to recompute it from name (duplicating _slugify + live_notes_dir logic), or ignore the return entirely.
• The type signature documents the intended behavior, so this is the smallest-surface fix — existing None returns on failure paths are preserved, so nothing downstream breaks.
• Prior commit f407429 ("R11 hotfix — return values, …") already swept similar gaps elsewhere; this looks like one that slipped through.

Test plan

• Added TestR16DuplicateEntities::test_track_new_returns_path which asserts the return value isinstance(result, Path), the file exists, and the path equals the expected live_notes_dir / slug.
• Existing assertions that expect None on failure are unchanged and still pass (test_track_duplicate_returns_none, test_track_empty_name, test_track_whitespace_name).
• Full suite: 278 passed locally (pytest tests/), up from 277.

Scope

This PR touches only track()'s success return and adds one test. No behavior change for any failure path, no refactor, no new dependencies.

🤖 Generated with Claude Code