Summary

Adds vendor-neutral content guardrail seams at the five boundaries where external content enters GBrain's retrieval layer and LLM gateway, so a content firewall (prompt-injection / RAG-poison detector, PII scrubber, etc.) can be hooked in without binding GBrain to any specific vendor.

Supersedes #1652 — rebased from garrytan-agents into a base-repo branch so CI gets secret access (per CLAUDE.md's "Checking out PRs from garrytan-agents" workflow). Original authorship preserved via cherry-pick; the feature commit is unchanged.

The seam, not the vendor. GBrain gets a generic runGuardrails({ hook, content, metadata }) interface with five hook points. Zero guardrails registered by default — the OSS ships completely inert. No vendor code, no API URL, no phone-home in the public tree. A provider (Silmaril or anyone) implements classify() in their own package and registers it at init.

Five hooks, all observe-only / fail-open:

• file_storage.markdown + file_storage.code — the import-into-retrieval boundary (the RAG-poison chokepoint)
• ai_gateway.chat / .expand / .tool_input — GBrain's own LLM calls

Hard invariants, test-enforced (14 tests): runGuardrails returns void so nobody can branch on a verdict; a throwing provider can't break an ingest; slow providers are awaited inline; empty content short-circuits. The existing import-file tests still pass — the hot path is undisturbed.

Closes the CVE gap. The injection-via-filesystem attack bypassed the old LLM-only hooks because content entered through the file boundary. file_storage.markdown is a real hook at that boundary now — the seam and the vuln fix are the same move.

Commits:

• feat(guardrails): vendor-neutral content guardrail seams (garrytan-agents) — the module, five hooks, doc, tests
• chore: bump version and changelog (v0.41.34.0)

Files

• src/core/guardrails.ts (new) — runGuardrails / registerGuardrailProvider / unregisterGuardrailProvider / hasGuardrails. Snapshot-before-iterate; per-provider try/catch.
• src/core/import-file.ts — file_storage.markdown (after parseMarkdown + size guard, before sanity/hash/chunk/embed/write) + file_storage.code (after code size guard, before hash/chunk/embed/write).
• src/core/ai/gateway.ts — ai_gateway.chat (latest user message only), ai_gateway.expand (query), ai_gateway.tool_input (tool name + input, before pending-persist). Cycle-safe stringifier.
• docs/guardrails.md (new) — contract, seam table, provider-authoring guide.
• test/guardrails.test.ts (new) — 14 tests pinning the contract.

Test Coverage

The seam is a new isolated module — test/guardrails.test.ts (14 tests) covers every invariant: observe-only (void return), fail-open (throw + reject isolation), inline await (slow async provider awaited), inert-by-default (zero providers = no-op), empty/blank short-circuit, register/unregister idempotency by id, content+metadata passthrough unmutated.

The five hook call sites are guarded by hasGuardrails() and wrapped fail-open, so with no provider registered they are pure no-ops — verified by the existing import-file suite (25 pass) and full typecheck.

Pre-Landing Review

bun run verify — 29/29 checks green. bun run typecheck clean. bun test test/guardrails.test.ts 14/14 pass. bun test test/import-file.test.ts 25/25 pass (ingest hot path undisturbed).

Documentation

docs/guardrails.md is the deliverable handed to integration partners: the contract (five hard invariants), the seam table, the provider-authoring guide, and a shadow-mode provider sketch. A partner's shadow-mode firewall becomes ~80 lines of provider code that never touches this public repo.

Test plan

• bun run verify — 29/29 green
• bun run typecheck — clean
• bun test test/guardrails.test.ts — 14/14 pass
• bun test test/import-file.test.ts — 25/25 pass (hot path undisturbed)

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