Drift check

Per-unit drift detection between each locked unit’s pinned SHA and its source’s current upstream tip. See .agents/goals/ainb-skill-manager-v1.2-rollup-plan.md §E for the full v1.2 spec this document summarises.

Why drift detection exists

Locked units pin a source SHA, but the upstream repo keeps moving. Before v1.2 there was no surface that said “the version you installed is 4 commits behind” — users had to run ainb skill update --check per-source. Drift detection replaces that with a single CLI + an always-on column in the SkillManager TUI.

Architecture

DriftBackend (trait)
└── GitLsRemoteBackend (production: `git ls-remote --`)
└── MockBackend         (tests: synthesise any DriftStatus variant)
        │
        ▼
DriftStatus { InSync | Outdated{behind} | Ahead{ahead} | Diverged{ahead,behind} }
        │
   ┌────┴────┐
   ▼         ▼
ainb skill check    SkillsScreenData::drift_cache
                                  │
                                  ▼
                            Units panel "status" column
                            (✓/⚠/▲/⟷ glyphs)

DriftDetector (E.1)

ainb_skill_core::drift::detect_drift(unit, source) -> Result<DriftStatus> delegates to a DriftBackend trait so production uses git ls-remote -- and tests inject a MockBackend that synthesises any of the four enum variants without network. The trait is Send + Sync so an Arc<dyn DriftBackend> can cross thread boundaries for the async background poll.

The production backend rejects repo URLs and refs that start with - and inserts an explicit -- argv terminator before positional values, closing the --upload-pack=<cmd> flag-smuggling vector.

ainb skill check CLI (E.2)

ainb skill check                  # report every locked unit
ainb skill check <source>         # scope to one source
ainb skill check --json           # machine-readable [{unit, status, ahead?, behind?}, …]

Default output is a fixed-width tabular report (unit, status), no external table dep. --json emits serde_json for scripts. Empty lockfile → # no units in lockfile. Out-of-scope source → # no units match the requested source.

Units panel status column (E.3)

SkillsScreenData::drift_cache: BTreeMap<String, DriftStatus> is keyed by UnitRow.declared_uri (new field in v1.2). The Units table renders the status as a glyph:

variant	glyph	colour
InSync	✓	green
Outdated	⚠	amber
Ahead	▲	cyan
Diverged	⟷	red
(missing from cache)	…	muted

The Detail pane shows the commit count under the active unit (for Outdated { behind: 4 } it reads 4 commits behind upstream).

Background drift poll (E.4)

GoToSkillManager triggers an async DriftBackend::detect_all (tokio spawn_blocking over the Arc<dyn DriftBackend> + an mpsc::unbounded_channel). Results land in drift_cache on the next AppState::tick. The table renders … placeholders until results arrive, so the screen stays interactive. A second GoToSkillManager while a poll is in flight coalesces — the second request is a no-op until the first lands.

Acceptance tripwires

• drift:: unit tests (14) — every variant reachable through the Mock backend; backend errors propagate.
• skill_check_tests (4) — tabular + JSON + --source scoping + empty-lockfile path.
• tripwire_core_skill_manager_drift_column (5) — every glyph + colour combination rendered.
• tripwire_core_skill_manager_drift_background_poll (2) — async fetch lands in drift_cache; second start coalesces.