# Implementation Plan: Inventory Core (040)

**Branch**: `spec/040-inventory-core` | **Date**: 2026-01-07 | **Spec**: `specs/040-inventory-core/spec.md`
**Scope (this step)**: Produce a clean, implementable `plan.md` + consistent `tasks.md` for Spec 040 only.

## Summary

Implement tenant-scoped Inventory + Sync Run tracking as the foundational substrate for later Inventory UI and higher-order features.

Key outcomes:

- Inventory is “last observed” (not backup), stored as metadata + whitelisted `meta_jsonb`.
- Sync runs are observable, selection-scoped via deterministic `selection_hash`.
- “Missing” is derived relative to latest completed run for the same `(tenant_id, selection_hash)`.
- Automation is safe: locks, idempotency, throttling handling, global+per-tenant concurrency limits.

## Technical Context

- **Language/Version**: PHP 8.4
- **Framework**: Laravel 12
- **Admin UI**: Filament v4 + Livewire v3
- **Storage**: PostgreSQL (JSONB available)
- **Queue/Locks**: Laravel queue + cache/Redis locks (as configured)
- **Testing**: Pest v4 (`php artisan test`)
- **Target Platform**: Sail-first local dev; container deploy (Dokploy)

## Constitution Check

- Inventory-first: inventory stores last observed state only (no snapshot/backup side effects).
- Read/write separation: this feature introduces no Intune write paths.
- Single contract path to Graph: Graph reads (if needed) go via Graph abstraction and contracts.
- Tenant isolation: all reads/writes tenant-scoped; no cross-tenant shortcuts.
- Automation: locked + idempotent + observable; handle 429/503 with backoff+jitter.
- Data minimization: no payload-heavy storage; safe logs.

No constitution violations expected.

## Project Structure (Impacted Areas)

```text
specs/040-inventory-core/
├── spec.md
├── plan.md
└── tasks.md

app/
├── Models/
├── Jobs/
├── Services/
└── Support/

database/migrations/
tests/Feature/
tests/Unit/
```

## Implementation Approach

### Phase A — Data Model + Migrations

1. Add `inventory_items` table
   - Identity: unique constraint to prevent duplicates, recommended:
     - `(tenant_id, policy_type, external_id)`
   - Fields: `display_name`, `platform`/`category` (if applicable), `meta_jsonb`, `last_seen_at`, `last_seen_run_id`.
   - Indexing: indexes supporting tenant/type listing; consider partials as needed.

2. Add `inventory_sync_runs` table
   - Identity: `tenant_id`, `selection_hash`
   - Status fields: `status`, `started_at`, `finished_at`, `had_errors`
   - Counters: `items_observed_count`, `items_upserted_count`, `errors_count`
   - Error reporting: stable error code(s) list or summary field.

### Phase B — Selection Hash (Deterministic)

Implement canonicalization exactly as Spec Appendix:

- Only include scope-affecting keys in `selection_payload`.
- Sort object keys; sort `policy_types[]` and `categories[]` arrays.
- Compute `selection_hash = sha256(canonical_json(selection_payload))`.

### Phase C — Sync Run Lifecycle + Upsert

- Create a service that:
  - acquires a lock for `(tenant_id, selection_hash)`
  - creates a run record
  - enumerates selected policy types
  - upserts inventory items by identity key
  - updates `last_seen_at` and `last_seen_run_id` per observed item
  - finalizes run status + counters
  - never creates/modifies snapshot/backup records (`policy_versions`, `backup_*`)

### Phase D — Derived “Missing” Semantics

- Implement “missing” as a computed state relative to `latestRun(tenant_id, selection_hash)`.
- Do not persist “missing” or “deleted”.
- Mark missing as low-confidence when `latestRun.status != success` or `latestRun.had_errors = true`.

### Phase E — Meta Whitelist

- Define a whitelist of allowed `meta_jsonb` keys.
- Enforce by dropping unknown keys (never fail sync).

### Phase F — Concurrency Limits

- Enforce global concurrency (across tenants) and per-tenant concurrency.
- The implementation may be via queue worker limits, semaphore/lock strategy, or both; the behavior must be testable.
- When limits are hit, create an observable run record with `status=skipped`, `had_errors=true`, and stable error code(s).

## Test Plan (Pest)

Minimum required coverage aligned to Spec test cases:

- Upsert identity prevents duplicates; `last_seen_*` updates.
- `selection_hash` determinism (array ordering invariant).
- Missing derived per latest completed run for same `(tenant_id, selection_hash)`.
- Low-confidence missing when latest run is partial/failed or had_errors.
- Meta whitelist drops unknown keys.
- Lock prevents overlapping runs per tenant+selection.
- No snapshot/backup rows are created/modified by inventory sync.
- Error reporting uses stable `error_codes` and stores no secrets/tokens.

## Out of Scope (Explicit)

- Any UI (covered by Spec 041)
- Any snapshot/backup creation
- Any restore/promotion/remediation write paths
