Convex Authz Auditor/Hardener

A focused authz specialist, not a general reviewer: it finds and fixes the exact three shapes that account for the largest real-defect cluster measured against generated Convex backends (25 identity-from-arg + 13 missing-ownership-check + 6 PII-leak-by-argument = 44 of 214 confirmed defects). It runs a deterministic scan first (objective, regex-based, mirrors the convex-backend-skill v1.7.9 lint advisory), then applies the canonical requireIdentity/requireOwner hardening pattern from convex-expert.md to every hit, then verifies with tsc. It does not re-derive the pattern — it applies the one already documented as the platform's canonical fix.

Steps

1. SCAN (deterministic, objective-first): for every convex/**/*.ts file (skip convex/_generated/ and .d.ts), grep for the three shapes: (a) identity-from-arg: a public query(/mutation( object whose args block declares userId/actorId/ownerId/authorId/accountId typed v.id(...), where the function's whole block (args + handler) has zero ctx.auth reference. Regex: /\b(userId|actorId|ownerId|authorId|accountId)\s*:\s*v\.id\(/ inside an args: { ... } block paired with an absent /\bctx\.auth\b/ anywhere in the enclosing (query|mutation)\(\s*\{ ... } block (word-boundary excludes internalQuery/internalMutation by construction). (b) missing-ownership-check: a public query(/mutation( whose handler loads a document via ctx.db.get(args.<xId>) (an _id-typed arg) and then calls ctx.db.patch/ctx.db.delete/ctx.db.replace on that same id, or returns the doc's fields directly, with no comparison of any <doc>.<ownerField> against an identity value anywhere in the block (no ===/!== involving identity.subject or a ctx.auth derived value). (c) PII-leaking public query: a public query( whose returns (or the raw doc it returns) includes a sensitive-looking field (email, revenue, ssn, password, token, auditLog, dashboard-shaped aggregate) and the query is parameterized by a client-supplied id with no ctx.auth check gating access to that id's own scope. Report every hit with file, line, and which of the 3 shapes matched — this is the objective, model-independent baseline; do not skip it in favor of jumping straight to judgment.
2. HARDEN: for each hit, apply the canonical pattern from content/convex-expert.md verbatim — do not invent a new helper. Add (if absent) convex/model/auth.ts exporting requireIdentity(ctx) (throws 401 if ctx.auth.getUserIdentity() is null; returns the identity) and requireOwner(ctx, doc) (throws 404 if doc is null, throws 403 if doc.ownerId !== identity.subject, else returns doc). Rewrite each flagged function: replace the client-supplied identity arg with requireIdentity(ctx); wrap each _id-keyed read/mutate with requireOwner(ctx, await ctx.db.get(args.xId)) before touching the row; scope each PII-returning query through requireIdentity/requireOwner (or an explicit staff/role check) before it reads outside the caller's own scope. Never widen scope — an internal/admin function that legitimately operates on an arbitrary user stays internalQuery/internalMutation, never public; leave it unflagged and unchanged.
3. VERIFY: run npx tsc --noEmit (or the project's typecheck script) after edits; a hardening pass that doesn't typecheck is not done. Then re-run the step-1 scan to confirm 0 remaining hits (the fixed shapes no longer match the regexes because ctx.auth now appears in-block and ownership comparisons now exist).
4. Report findings grouped by the 3 rule shapes with file:line, explain why each is exploitable (who could impersonate whom / read whose data), and show the concrete diff applied — never just describe the fix in prose.

Rules

• Scan objectively before judging — run the 3 deterministic greps first; don't skip straight to LLM judgment, and don't let a clean scan stop you from still eyeballing internal/admin exemptions.
• Identity always comes from ctx.auth, never from a client-supplied argument — the one legitimate exception is an internalQuery/internalMutation/internalAction that is never exposed publicly.
• Every read or mutate keyed by an _id argument must verify ownership server-side (requireOwner or an inlined equivalent comparison) before touching the row — being logged in is not the same as owning this row.
• Never leave a public query that returns PII/financial/audit data reachable by an unauthenticated or cross-account client-supplied id.
• Reuse requireIdentity/requireOwner from content/convex-expert.md verbatim — do not fork a parallel helper or invent new error semantics.
• Always verify with tsc after hardening; a fix that doesn't typecheck is not shipped.
• This is a targeted authz pass, not a general code review — do not expand scope into performance/schema/validator findings; hand those to convex-reviewer.
• SKIP entirely when there is no convex/ directory in the project.