---
id: review-002-fwd17-19-contract-decisions
name: Forwarding contract decisions — non-JSON SSE payloads, double-routed placeholders, percent preservation (FWD-17/18/19 decide+document or fix)
status: completed
depends_on: [review-002-fwd15-stream-timeout]
scope: narrow
risk: low
impact: component
level: implementation
tags: [adapters, review-002, from-openapi]
---

## Description

Three review-002 forwarding findings that are design decisions more
than bugs — decide, document, and fix where the decision says so:

- **FWD-17**: non-JSON SSE payloads silently degrade to JSON strings
  (`forward.rs:774-781`, `unwrap_or(Value::String)`) and the parser's
  `event:` field is discarded (`:977-979`). A consumer cannot extract
  fields from a legitimately non-JSON stream, and an upstream's
  SSE `event: error` convention is indistinguishable from data.
  Decide: (a) document the JSON-or-string contract as-is, or (b) carry
  the raw payload + the `event:` field name in the envelope for
  non-JSON payloads (e.g. `{data, event}` object wrapper).
- **FWD-18**: non-scalar path-placeholder values double-route —
  rendered into the path (as JSON text) *and* appended as a query
  param (`forward.rs:144-157`). Fix the routing rule: a key that
  matched a placeholder never also emits as query, regardless of value
  shape (plus a spec-decision on whether object/array path values are
  an error instead).
- **FWD-19 [info]**: preserved literal `%` in template/base text is
  upstream-semantics-changing (`%2F` survives; most stacks route it
  differently from `/`). Inputs are assembly-supplied (ADR-066 trust);
  document the trade-off in the module doc (+ ADR-066 note) — or
  reject raw `%` in *template text* while allowing it in values
  (the strict shape).

## Acceptance Criteria

- [ ] A decision per finding, recorded (module doc + ADR-066 section
      as appropriate); doc-only outcomes still need the doc change +
      a doc-asserting test where applicable
- [ ] FWD-17: whichever shape is chosen, non-JSON payload behavior is
      pinned by a test (string case, number-vs-string distinction,
      event-field presence if option (b))
- [ ] FWD-18: placeholder keys never double-emit (query test with an
      object value under a placeholder key) — and the object-in-path
      outcome (error vs JSON-segment) decided and tested
- [ ] FWD-19: documented (and if the reject-raw-% shape is chosen, its
      import- or call-time error tested)
- [ ] `cargo test`, `cargo clippy --all-targets -- -D warnings`,
      `cargo fmt --check` pass

## References

- docs/reviews/002-post-remediation-review.md (Part D', FWD-17/18/19)
- src/adapters/forward.rs:774-781, :977-979, :144-157, :353-370, :481-505
- docs/architecture/decisions/066-from-jsonschema-as-http-adapter.md
- tasks/adapters/review-002-fwd13-dot-segments.md (adjacent template-renderer work — sequence or coordinate to avoid churn in the same helpers)

## Notes

Deliberately a decide-first task: none of the three is a crash or
leak; each is a contract the code half-implies. Keep the decisions
small and documented rather than building speculative machinery (e.g.
no new envelope schema unless (b) is actually chosen). Coordinate with
review-002-fwd13-dot-segments (same helpers, different concerns).

## Summary

FWD-17: non-JSON SSE payloads surface as {data, event} wrapper (event: captured, WHATWG last-wins, leak fixed). FWD-18: structural placeholder values are INVALID_INPUT (no JSON splicing into paths). FWD-19: % in values always encoded, template text preserves pre-encoded % (ADR-066 trust boundary). ADR-066 records all three; SseEvent gained an event field (crate-internal).