Bug: workspace hash changed from MD5 to SHA256 between versions, silently breaking @memory for existing users

[tcconnally]

Users upgrading from older Perseus versions (pre-v1.0.3) will find @memory silently returning 'No Mnēmē narrative found' because the workspace hash algorithm changed from MD5 to SHA256. Existing narrative files are stored under the MD5-based filename (e.g. faafba882994.md) but Perseus now expects SHA256 (e.g. a7b1f892fc76.md).

Steps to reproduce:

1. Have a Perseus install with a narrative created under an older version
2. Upgrade to v1.0.3+
3. Run perseus memory show → 'No Mnēmē narrative found'
4. Run @memory in a render → same error

Expected

Migration guide or automatic detection/migration of old hash-named files

Actual

Silent failure with unhelpful error message

Workaround

Manually compute SHA256 hash of workspace path and copy the narrative file to the new name, update frontmatter workspace_hash field.

Suggested fix

On startup/memory commands, check for MD5-named files and either auto-migrate or emit a specific 'legacy narrative found, run perseus memory migrate' message.

[tcconnally]

Code review verification (v1.0.3)

Confirmed bug. _mneme_path in src/perseus/mneme_narrative.py:39–42 computes only the SHA-256 path with no legacy-MD5 fallback:

def _mneme_path(workspace: Path, cfg: dict) -> Path:
    store = Path(cfg.get('memory', {}).get('store', str(PERSEUS_HOME / 'memory')))
    return store / f'{_workspace_hash(workspace)}.md'

Suggested patch

def _mneme_path(workspace: Path, cfg: dict) -> Path:
    store = Path(cfg.get('memory', {}).get('store', str(PERSEUS_HOME / 'memory')))
    new_path = store / f'{_workspace_hash(workspace)}.md'
    if new_path.exists():
        return new_path
    try:
        canonical = str(workspace.expanduser().resolve())
        legacy = store / f'{hashlib.md5(canonical.encode()).hexdigest()[:12]}.md'
        if legacy.exists():
            store.mkdir(parents=True, exist_ok=True)
            os.replace(legacy, new_path)
    except OSError:
        pass
    return new_path

Also surface perseus memory doctor --migrate that walks <store>/*.md, parses the workspace: frontmatter field, recomputes the SHA-256 hash, and renames orphaned files.

Related new findings: #157 (bump hash to 16 chars for federation safety).

[tcconnally]

Fixed in PR #179 (integration branch targeting main).