---
id: review-001-ref-cycle-guard
name: Bounded, cycle-safe $ref resolution (OAI-01, OAI-08)
status: completed
depends_on: []
scope: narrow
risk: high
impact: component
level: implementation
tags: [adapters, review-001, from-openapi]
---

## Description

Review 001 finding OAI-01 — the single highest-severity finding in the
review (borderline critical, empirically verified):
`resolve_refs_recursive` (`src/adapters/openapi_spec.rs:199-221`) recurses
with no cycle detection and no depth budget. A self-referential component
(`{"$ref":"#/components/schemas/Node"}` inside Node — trees, linked
lists, cursor pagination: common and *valid* OpenAPI) recurses until the
stack is exhausted: `thread has overflowed its stack; fatal runtime
error` → **process abort**. Not a catchable panic; `import()` kills the
whole process — startup crash-loop, or remote DoS if specs are ever
runtime-refreshed/peer-supplied.

Fix: depth budget + visited set keyed on the JSON-pointer path, returning
a clean `CallError`/import error on cycles and over-deep specs. **Do not**
try to preserve full recursive expansion of recursive schemas — the goal
is a clean, loud error (or a depth-limited expansion where the adapter can
safely represent it), not unbounded expansion.

Ride-along: **OAI-08** — guarded `expect`s in `openapi_spec.rs:144,170`
(the "no `expect` outside tests" convention; `if let` costs nothing).

## Acceptance Criteria

- [x] Import of a self-referential spec returns an error — the process does not abort (the review's named acceptance gate: a test importing a self-referential spec would have caught the abort immediately)
- [x] Deeply-nested non-circular spec beyond the budget errors cleanly at import (test)
- [x] A non-recursive spec with `$ref` sharing (refs to a common schema) still imports identically — no false cycle positives (existing suite green)
- [x] OAI-08 `expect`s replaced
- [x] `cargo test` and `cargo clippy --all-targets -- -D warnings` pass

## References

- docs/reviews/001-initial-implementation-review.md (Part E, OAI-01, OAI-08)

## Notes

> Agent fills during implementation. Do before anything
> deployment-facing. Deliberately split from the parameter/requestBody
> work (review-001-openapi-import-integrity) so the delicate
> cycle-detection change lands alone.

Implementation decisions:

- Depth budget set to 64 (`MAX_REF_RESOLUTION_DEPTH`, pub(crate) const in
  openapi_spec.rs) — far above any legitimately expandable schema height,
  2× serde_json's parse recursion limit. It bounds both `$ref` hop chains
  and plain schema nesting.
- Clean loud error chosen over depth-limited expansion, per the task's
  stated preference: recursive schemas (trees, linked lists, cursor
  pagination) fail import with `AdapterError::SchemaParse` naming the
  offending ref, rather than expanding unboundedly or truncating
  silently.
- The visited set is branch-scoped (insert before recursing, remove on
  return), so shared refs to one common schema — diamond or repeated —
  resolve normally; only a ref re-entering its own expansion chain is a
  cycle.
- OAI-08: both guarded `expect`s (`paths is object`, `schemas is
  object`) replaced with `if let Some(..)`; the inner-body re-shape is
  behavior-preserving (both sites were immediately preceded by an
  `is_object()` check).
- Tests added in `src/adapters/openapi_spec.rs` (`mod tests`): direct
  recursive + mutually-recursive error, over-deep non-circular error, two
  no-false-positive cases (shared common schema, diamond reuse), and an
  end-to-end `FromOpenAPI::import` of a self-referential spec asserting
  an error return (process does not abort).

## Summary

Implemented bounded, cycle-safe `$ref` resolution in
`src/adapters/openapi_spec.rs` (review 001 OAI-01 + OAI-08):
`resolve_refs_recursive` now delegates to a `resolve_refs_bounded`
worker carrying a branch-scoped `HashSet` of in-flight JSON-pointer refs
and a depth counter against `MAX_REF_RESOLUTION_DEPTH` (64). A ref
re-entering its own expansion chain errors with
`AdapterError::SchemaParse` ("circular $ref detected …: <ref>"); a
ref-chain or nesting height beyond the budget errors similarly ("exceeded
depth budget of 64"). Import of a self-referential spec therefore
returns a clean import error instead of aborting the process via stack
overflow (OAI-01); OAI-08's two guarded `expect`s in `from_value` became
plain `if let` paths. Six tests added in `openapi_spec.rs` covering the
cyclic, over-deep, and shared-ref matrices plus the named acceptance
gate (end-to-end self-referential import errors, no abort). 188 lib
tests green; full `cargo test`, `cargo clippy --all-targets -- -D
warnings`, and `cargo fmt --check` pass.