docs(skills): spec + plan for per-level session skills

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Mika Kuns
2026-07-23 16:47:14 +02:00
committed by mika kuns
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# Session Skills — Design
**Date:** 2026-07-03
**Status:** Approved (design), implementation not started
## Problem
Mika wants to give headless task agents a specific Claude skill (e.g.
[ponytail](https://github.com/DietrichGebert/ponytail)) **without** installing it
globally in `~/.claude/skills/`, where it would leak into every interactive session.
Skills should be a first-class, per-level session setting alongside `model`,
`max_turns`, and `system_prompt` — configurable **global / per-list / per-task** — and
sourced from a GitHub URL.
## Key facts that shape the design
- The Claude CLI discovers skills from two places: the **global** `~/.claude/skills/`
(every session — undesirable here) and the **working directory's** `.claude/skills/`
(plus plugins). ClaudeDo fully controls each spawned session's `WorkingDirectory`
(`ClaudeProcess.cs:30`), so a skill dropped into the session cwd is scoped to exactly
that headless run.
- **Auto-commit uses `git add -A`** (`WorktreeManager.CommitIfChangedAsync`
`_git.AddAllAsync`, `WorktreeManager.cs:142`). Anything seeded into a worktree's
`.claude/skills/` would be committed unless explicitly excluded → the seeder must add
the seeded paths to the worktree's `info/exclude`.
- A skill is not just prompt text: `SKILL.md` may reference scripts that run via Bash.
Headless agents run with `--permission-mode auto` (effectively unattended), so a skill
pulled from an arbitrary URL is **unattended third-party code execution**. This is why
install is a deliberate, pinned, reviewable step — not a live per-run URL fetch.
## Decisions (locked)
1. **Install-and-pin, not live fetch.** A dedicated registry screen installs a skill
once: clone the repo, pin to the current commit, store locally. Per-level config then
references installed skills **by name** (checkboxes), never a URL.
2. **Three levels, additive union.** Effective skill set = `global list task`.
(Unlike `model`/`prompt`, which override — skills add up. Trade-off accepted: an
inherited skill can't be switched off for a single task in the MVP.)
3. **One repo = one skill.** Installer accepts only a repo with `SKILL.md` at the root
(covers ponytail). Multi-skill repos / plugin-format repos are out of scope for MVP.
4. **Public repos only** (plain `git clone` over HTTPS, no auth) for MVP.
## Architecture
### Storage & registry
- Installed skills live at `~/.todo-app/session-skills/<name>/` (the cloned repo contents,
`SKILL.md` at root).
- New DB table `session_skills`: `name` (PK), `source_url`, `pinned_ref` (commit SHA),
`description`, `added_at`.
- New worker service `SessionSkillRegistry` (in a new `Skills/` area under the Worker):
- `InstallAsync(url)` — clone to temp → validate `SKILL.md` at root → parse frontmatter
(`name`, `description`) → resolve HEAD SHA as `pinned_ref` → move into place →
upsert DB row. Name collision → error surfaced to UI. The clone step is injected
(`IRepoCloner`) so tests use a local source dir — **no real network, no real CLI**.
- `UpdateAsync(name)` — re-fetch, checkout latest, refresh files + `pinned_ref`.
- `RemoveAsync(name)` — delete dir + row.
- `ListAsync()` — registry entries for the UI.
### Resolution
`TaskRunner.ResolveConfigAsync` (`TaskRunner.cs:488`) already merges
task → list → global for the other fields. Add:
```
SkillNames = Union(task.SessionSkills, listConfig?.SessionSkills, global.SessionSkills)
```
deduped, filtered to names that still exist in the registry (a removed skill is silently
dropped — logged). Add `IReadOnlyList<string> SkillNames` to `ClaudeRunConfig`
(`ClaudeArgsBuilder.cs:5`). **No CLI flag is emitted** — skills are seeded on disk, not
passed as args. `ClaudeArgsBuilder.Build` is unchanged for skills.
Per-level storage: a nullable TEXT column `session_skills` (JSON array of names) on
`tasks`, `list_config`, and `app_settings`.
### Seeding
New service `SessionSkillSeeder`, called by `TaskRunner` after the working dir is
resolved and before `ClaudeProcess.RunAsync`:
- For each resolved skill name, copy `~/.todo-app/session-skills/<name>/`
`<cwd>/.claude/skills/<name>/` (overwrite → idempotent for resume/re-run).
- If the cwd is a git worktree, append `/.claude/skills/<name>/` to the worktree's
`info/exclude` (path via `git rev-parse --git-path info/exclude`, so it targets the
per-worktree exclude), only if not already present. **Only the seeded subdirs are
excluded** — never blanket-exclude `/.claude/`, in case the target project commits its
own `.claude/`.
- Sandbox runs (not a repo) skip the exclude step.
- No separate cleanup: seeded dirs vanish with the worktree/sandbox.
### allowedTools caveat
`--allowedTools` is only emitted when set (`ClaudeArgsBuilder.cs:80`); normal task runs
leave it null → all tools allowed → the `Skill` tool is available. If a future per-task
allowedTools restriction is added, it must include `Skill`. Noted, not handled in MVP.
## UI
Mirror the existing agent-file pattern.
- **Registry screen ("extra mask"):** a new **Skills** tab in the Settings modal
(`SettingsModalView.axaml`) with `SessionSkillsSettingsTabViewModel`. Lists installed
skills (name, description, source, short ref); **Add** (URL text box → install),
**Update**, **Remove**. Status/error line like `FilesSettingsTabViewModel`.
- **Global selector:** multi-select (checkbox list) of installed skills in the General
settings tab → `AppSettings.SessionSkills`.
- **List + Task selectors:** add a skills multi-select to the shared
`AgentConfigEditor` control (`AgentConfigEditor.axaml` /
`AgentConfigEditorViewModel.cs`), which is already reused by both List settings and the
per-task flyout — one addition covers both levels, with the existing inheritance-badge
pattern.
### Hub / client surface
New `WorkerHub` methods + `IWorkerClient` entries (update hand-rolled fakes in both test
projects — see memory `iworkerclient_fakes_sync`):
`GetSessionSkills`, `InstallSessionSkill(url)`, `UpdateSessionSkill(name)`,
`RemoveSessionSkill(name)`. Extend `AppSettingsDto`, `ListConfigDto`,
`UpdateListConfigDto`, `UpdateTaskAgentSettingsDto` with the selected skill-name lists.
New `SessionSkillDto`.
## Edge cases
- **Removed skill still referenced** by a level → dropped at resolve time, logged, no
failure.
- **Name collision on install** → reject with a clear message; offer Update instead.
- **Repo without root `SKILL.md`** → reject at install.
- **Target project already has `.claude/skills/`** → additive copy; exclude only our
subdirs.
- **Resume / re-run** reuses the worktree → re-seed overwrites, exclude append is
idempotent.
## Verification (must-check, can't be unit-tested)
- **Does `claude -p` actually load and invoke a skill placed in cwd `.claude/skills/`?**
This is the load-bearing assumption. Manual smoke test with ponytail before calling the
feature done. If headless mode does *not* surface cwd skills, fall back to
`CLAUDE_CONFIG_DIR` isolation (heavier — needs credentials copied) and revisit.
- Seeded skill is **not** committed by the auto-commit step (worktree run).
- Skill does not appear in a normal interactive session (no global leak).
## Out of scope (MVP)
Private-repo auth; multi-skill / plugin-format repos; auto-update & update notifications;
per-task *disabling* of an inherited skill; surfacing skill invocation in the run log.