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16dc7c Claude (MCP) 2026-03-17 16:47:00
[mcp] Add disk usage caps implementation plan
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---
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category: spec
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tags: [quota, disk-usage, plugin, plan]
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last_updated: 2026-03-17
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confidence: high
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---
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# Per-Wiki Disk Usage Caps Plan
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Quota enforcement code already exists in `resolver.py` (50MB limit, write rejection) but reads from `robot.db` where `disk_usage_bytes` is always 0. This plan wires up real measurements.
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## Architecture
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- **Measurement:** `du -sb` on entire wiki directory (repo + wiki.db + FAISS index)
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- **Storage:** New `stats` table in per-wiki `wiki.db` (not robot.db) — resolver already operates per-wiki-DB
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- **Update timing:** Page count on every save/delete (via otterwiki plugin hook). Disk usage via cron only (15-min interval, acceptable lag).
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- **Enforcement:** Existing resolver code — reads stats from `wiki.db` after DB swap, strips WRITE permission or returns 413 for API requests.
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## Components
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### 1. `stats` table in `wiki.db`
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```sql
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CREATE TABLE IF NOT EXISTS stats (
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name VARCHAR(64) PRIMARY KEY,
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value TEXT,
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updated_at DATETIME
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);
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```
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Keys: `page_count`, `disk_usage_bytes`. Seeded in `_init_wiki_db()`.
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### 2. New plugin: `otterwiki-wikistats`
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Follows `otterwiki-api` pattern. Hooks: `page_saved`, `page_deleted` → update `page_count` via `storage.list()`. Disk usage left to cron. Must use `_state["storage"]` dict (not `self.storage`) for multi-tenant correctness — resolver patches this in `_swap_storage()`.
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### 3. Resolver changes
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- Add `_get_wiki_stats(wiki_dir)` — reads `stats` table from `wiki.db`
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- Move quota check to after `_swap_database()` — read real disk_usage from `wiki.db` with fallback to `robot.db`
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- Add `otterwiki_wikistats._state["storage"]` patch in `_swap_storage()`
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- Seed `stats` table in `_init_wiki_db()`
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### 4. Cron backstop update
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Update `wiki-quota.sh.j2` to write to each wiki's `wiki.db` stats table (primary) AND keep updating `robot.db` for the dashboard API.
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## User Experience
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- **API/MCP:** HTTP 413 with `"Wiki quota exceeded (50MB limit)"`
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- **Web UI:** 403 on save (WRITE stripped). Generic permission denied — quota-specific message is a follow-up.
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- **Dashboard:** Reads `disk_usage_bytes` from `robot.db` via management API (15-min lag from cron).
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## Files to Modify
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| Repo | File | Change |
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|---|---|---|
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| robot.wtf | `app/resolver.py` | `_get_wiki_stats()`, quota check after swap, stats table in init, storage patch |
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| robot.wtf | `ansible/roles/quota/templates/wiki-quota.sh.j2` | Write to wiki.db + robot.db |
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| robot.wtf | `ansible/roles/deploy/tasks/main.yml` | pip install otterwiki-wikistats |
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| new repo | `otterwiki-wikistats` | Plugin: setup, page_saved, page_deleted hooks |
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## Test Plan
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1. Quota read from wiki.db — over limit → WRITE stripped
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2. Under limit → pass-through
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3. API over-quota → 413
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4. Fallback to robot.db when stats table missing
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5. Plugin: page count updated on save/delete
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6. Plugin: uses `_state["storage"]` not stale reference
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## Open Questions
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1. Quota check must move to after `_swap_database()` — verify no regression on API 413 path
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2. Cron user permissions on wiki.db files
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3. Plugin `_state` dict convention — follow existing pattern from `otterwiki-api`