fix(codex): survive OpenAI's strict validator on --output-schema

[AbirAbbas]

Fixes #106

Summary

The server behind codex exec now validates --output-schema against OpenAI strict-mode rules and 400s non-strict schemas with invalid_json_schema — killing every schema-enforced codex role (PM, git init, …) in seconds, on both nodes.

Contrary to the issue's follow-up comment, this is not a blanket rejection of the flag: live probing on the same codex-cli 0.144.1 + ChatGPT-account auth shows a fully strict schema is ACCEPTED (the trivial repro schema was missing additionalProperties: false, which the validator now demands on every object node). The real gaps were in our strict rewrites:

• free-form maps (dict[str, Any] → {"type": "object"} with no properties) never get additionalProperties: false, and strict mode cannot express them at all without forcing {} output
• Any-typed fields emit bare {} nodes — rejected with "schema must have a 'type' key" (and on the Go node, boolean true subschemas — the generic "Please ensure it is a valid JSON Schema" 400 from the issue report)
• typed maps (additionalProperties: {schema}) are rejected outright

Changes Made (Python node)

Two layers in swe_af/runtime/codex_harness_patch.py:

• Deterministic gate — _codex_schema_strict_expressible checks the written strict schema against the live-probed validator rules before adding --output-schema. Inexpressible schemas run with --output-last-message only: codex still persists its final JSON and the harness runner's existing local validation enforces the schema (exactly the "prompt-embedded JSON + local validation" fallback proposed in the issue).
• Reactive fallback — if the server refuses a schema anyway (its rules can tighten upstream at any time), the run is retried once without --output-schema, keeping --output-last-message.

Go node

The Go node's equivalent lives in the agentfield Go SDK's codex provider/runner — fixed by Agent-Field/agentfield#818 (same gate + fallback design, live-verified: the strict rewrites of the real GitInitResult/Architecture schemas are ACCEPTED by the validator, PRD is correctly gated). Once that merges, an SDK re-pin PR here (go.mod pseudo-version + AGENTFIELD_SDK_REF in ci.yml / go/Dockerfile) completes #106 for the Go node.

Testing

• 6 new tests: expressibility accept/reject table (free-form map, typed map, bare Any, boolean subschema, poisoned $defs, object in a type list), rejection→rerun flow, inexpressible-schema flag skip, no-rerun on unrelated failure.
• Full suite: 1135 passed, 1 skipped (pre-existing); compileall clean.
• Validator rules established by live probes against codex exec --output-schema (10 schema shapes), not guesswork.

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