feat(auth): capability check — user/cron/worker allow; agents tiered allow/suggest/deny

docs/security-followups.md

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+# Security Follow-ups for Plan 1
+
+Items flagged by the security review plugin that were deferred at the user's request
+("ease up on the security plugin") and are to be addressed in a consolidated pass
+before Plan 1 is declared complete.
+
+## Migration 005 (cross-cutting / polymorphic tables)
+
+The polymorphic shape (`entity_type` text + `entity_id` uuid, no composite FK to a
+parent) was an approved design decision in `docs/superpowers/specs/2026-05-31-void-v2-design.md`.
+That decision trades referential integrity at the DB layer for one shared join table
+across entity types. The plugin's findings are accurate but require revisiting the
+design choice — not a one-line fix.
+
+- **[HIGH] entity_tags / entity_links / attachments lack `space_id`.**
+  Cross-tenant linkage is possible at the DB layer. Mitigation options:
+    1. Add `space_id` NOT NULL to each polymorphic row; require callers to filter.
+    2. Per-type junction tables (e.g. `page_tags`, `task_links`) with real FKs.
+
+- **[MEDIUM] `tags.name UNIQUE` is global, not per-space.** Cross-tenant collision
+  creates a side-channel for tag-name discovery. Fix: `UNIQUE(space_id, name)`.
+
+- **[MEDIUM] No cascade on parent delete for `attachments` / `entity_tags`.**
+  Polymorphic FKs cannot be expressed in standard SQL. Fix options as above, or
+  a deletion trigger per parent type.
+
+## Decision pending
+
+Before closing Plan 1, decide whether to:
+- (a) **Tighten now**: add `space_id` columns + per-type composite FKs to `entity_tags`,
+  `entity_links`, `attachments`, and a per-space UNIQUE on `tags`. Cost: ~1-2 hrs and
+  invalidates the polymorphic claim in the spec.
+- (b) **Document and defer**: accept the tradeoff for Plan 1, gate access at the
+  REST/MCP layer (where `space_id` IS available from the actor's session), and
+  revisit when multi-tenant becomes load-bearing.
+
+Owner-only authn (Plan 1) means there's only one tenant in practice today, so (b) is
+defensible for the alpha. (a) is the right long-term answer.

lib/auth/capability.js

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+export function canAct(actor, action, entity_type) {
+  if (!actor) return 'deny';
+  if (actor.kind === 'user') return 'allow';
+  if (actor.kind === 'cron' || actor.kind === 'worker' || actor.kind === 'system') return 'allow';
+
+  if (actor.kind !== 'agent') return 'deny';
+
+  const caps = actor.capabilities || {};
+  const scopes = actor.scopes || {};
+
+  if (action === 'read') return caps.read ? 'allow' : 'deny';
+
+  const isMutation = ['create','update','delete'].includes(action);
+  if (!isMutation) return 'deny';
+
+  if (caps.write && scopes[entity_type]) return 'allow';
+  if (caps.suggest) return 'suggest';
+  return 'deny';
+}

tests/auth/capability.test.js

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+import { describe, it, expect } from 'vitest';
+import { canAct } from '../../lib/auth/capability.js';
+
+const ownerActor = { kind: 'user', id: null };
+const readAgent = {
+  kind: 'agent', id: 'a1',
+  capabilities: { read: true, suggest: true, write: false },
+  scopes: {}
+};
+const writeAgent = {
+  kind: 'agent', id: 'a2',
+  capabilities: { read: true, suggest: true, write: true },
+  scopes: { page: true }
+};
+
+describe('canAct', () => {
+  it('owner can do anything', () => {
+    expect(canAct(ownerActor, 'create', 'page')).toBe('allow');
+    expect(canAct(ownerActor, 'delete', 'resource')).toBe('allow');
+  });
+
+  it('read-only agent can read', () => {
+    expect(canAct(readAgent, 'read', 'page')).toBe('allow');
+  });
+
+  it('default agent on create returns "suggest"', () => {
+    expect(canAct(readAgent, 'create', 'page')).toBe('suggest');
+  });
+
+  it('write-scoped agent can write to its scope', () => {
+    expect(canAct(writeAgent, 'create', 'page')).toBe('allow');
+  });
+
+  it('write-capable agent without scope still suggests outside it', () => {
+    expect(canAct(writeAgent, 'create', 'resource')).toBe('suggest');
+  });
+
+  it('agent with no capabilities is deny on mutations', () => {
+    expect(canAct({ kind: 'agent', id: 'x', capabilities: {} }, 'create', 'page')).toBe('deny');
+  });
+
+  it('agent with no read capability is deny on read', () => {
+    expect(canAct({ kind: 'agent', id: 'x', capabilities: {} }, 'read', 'page')).toBe('deny');
+  });
+
+  it('null actor is deny', () => {
+    expect(canAct(null, 'read', 'page')).toBe('deny');
+  });
+
+  it('cron/worker/system get allow', () => {
+    expect(canAct({ kind: 'cron', id: null }, 'create', 'page')).toBe('allow');
+    expect(canAct({ kind: 'worker', id: null }, 'update', 'page')).toBe('allow');
+    expect(canAct({ kind: 'system', id: null }, 'delete', 'page')).toBe('allow');
+  });
+});