---
issue: 9
title: Core session module — save, load, list, word cap
status: done
failure_log: null
tags:
  - type/story
  - status/done
---

## Implementation

Create `src/mantle/core/session.py` with a read/write interface for session logs. Session logs record what was done, decisions made, and what's next. Follows the same module patterns as `core/challenge.py` and `core/learning.py`.

### src/mantle/core/session.py

```python
"""Session logging — structured records of work done, decisions, and next steps."""
```

#### Data model

```python
class SessionNote(pydantic.BaseModel, frozen=True):
    project: str
    author: str
    date: datetime
    commands_used: tuple[str, ...]
    tags: tuple[str, ...] = ("type/session-log",)
```

Note: This is the first core module to use `datetime` (not `date`) since session logs include time of day.

#### Constants

```python
WORD_CAP: int = 200
```

#### Warning

```python
class SessionTooLongWarning(UserWarning):
    """Issued when a session log exceeds the ~200 word cap."""
```

#### Functions

- `save_session(project_dir, content, *, commands_used=()) -> tuple[SessionNote, Path]` — Write session log to `.mantle/sessions/<date>-<HHMM>.md`. Reads project name from `state.load_state()`. Resolves author via `state.resolve_git_identity()`. Timestamps with `datetime.now()`. Issues `SessionTooLongWarning` via `warnings.warn()` if body exceeds `WORD_CAP`. Returns frontmatter note and written path.

- `load_session(path) -> tuple[SessionNote, str]` — Read a session log via `vault.read_note()`. Returns (frontmatter, body). Raises `FileNotFoundError` if path doesn't exist.

- `list_sessions(project_dir, *, author=None) -> list[Path]` — List all session logs in `.mantle/sessions/`, sorted oldest-first. If `author` is provided, filter to sessions matching that author by reading each file's frontmatter.

- `session_exists(project_dir) -> bool` — True if at least one session log exists. Convenience wrapper: `len(list_sessions(project_dir)) > 0`.

- `count_words(text) -> int` — Count words in text. `len(text.split())`.

#### Internal helpers

- `_resolve_session_path(project_dir) -> tuple[Path, datetime]` — Generate the session log path from current datetime. Format: `.mantle/sessions/<date>-<HHMM>.md` (e.g., `2026-02-22-1430.md`). Auto-increments on collision: `-2`, `-3`, etc. Creates `sessions/` directory if missing (`mkdir(parents=True, exist_ok=True)`). Returns both the resolved path and the datetime used so `save_session` stores the exact timestamp in frontmatter.

#### Imports

```python
from mantle.core import state, vault
```

#### Design decisions

- **No state transition.** Session logs are passive records. They don't change the project's workflow state.
- **No state body update.** Unlike idea/challenge/design modules, session logs don't update state.md's Current Focus section. Sessions are ambient context, not workflow steps.
- **Project name read from state.md.** `state.load_state(project_dir).project` ensures consistency with the project identity.
- **Author filter on list.** Supports the system design requirement that `/mantle:resume` filters session logs to the current user's `git config user.email`.
- **Warning, not error, for word cap.** The ~200 word cap is a guideline enforced primarily by Claude instructions. The code warns via `warnings.warn()` but doesn't reject content.
- **datetime, not date.** Session logs need time resolution to the minute for meaningful chronological ordering. The filename encodes `HHMM` and the frontmatter stores full `datetime`.

## Tests

### tests/core/test_session.py

All tests use `tmp_path` fixture with a pre-created `.mantle/sessions/` directory and `state.md` at any status. Mock `state.resolve_git_identity()` to return a fixed email.

- **save_session**: writes file to `.mantle/sessions/` directory
- **save_session**: filename matches `<date>-<HHMM>.md` pattern
- **save_session**: correct frontmatter fields (project, author, date, commands_used, tags)
- **save_session**: round-trip with `load_session` preserves frontmatter
- **save_session**: round-trip preserves body content
- **save_session**: stamps author with git identity
- **save_session**: project field matches state.md project name
- **save_session**: date field is a datetime (includes time, not just date)
- **save_session**: commands_used stored as tuple
- **save_session**: empty commands_used defaults to empty tuple
- **save_session**: default tags are `("type/session-log",)`
- **save_session**: warns `SessionTooLongWarning` when body exceeds WORD_CAP
- **save_session**: no warning when body is under WORD_CAP
- **save_session**: auto-increments filename on collision (same minute)
- **load_session**: reads saved session correctly
- **load_session**: raises `FileNotFoundError` when path doesn't exist
- **list_sessions**: returns empty list when no sessions
- **list_sessions**: returns sorted paths (oldest first)
- **list_sessions**: filters by author when specified
- **list_sessions**: returns all sessions when author is None
- **session_exists**: returns False when no sessions
- **session_exists**: returns True after saving a session
- **count_words**: counts words in simple text
- **count_words**: returns 0 for empty string
- **SessionNote**: frozen (cannot assign to attributes)
