Best possible solution:

Use #100801 as the landing path for the cron tool schema fix, then close the linked issue when that proof-positive PR lands with green required checks.

Do we have a high-confidence way to reproduce the issue?

Yes by source inspection. Current main keeps patch.payload.fallbacks non-null in createCronToolSchema(), while the gateway schema and service merge path already accept and clear null fallbacks.

Is this the best way to solve the issue?

No for this branch as the landing path. The runtime code shape is plausible, but #100801 already owns the same fix with stronger proof, while this branch lacks real behavior proof and prompt snapshot updates.

Security review:

Security review cleared: The diff only changes TypeBox schema wiring and focused tests; it adds no dependencies, scripts, permissions, secret handling, or supply-chain surface.

AGENTS.md: found and applied where relevant.

What I checked:

• Current main still has the reported cron tool schema gap: On current main, cronPayloadObjectSchema hardcodes fallbacks as an optional string array while the update patch path only parameterizes nullable model and toolsAllow, so the linked bug is a real tool-schema issue rather than a config-schema issue. (src/agents/tools/cron-tool.ts:123, 41bea62b4a28)
• Gateway protocol and service already support null fallback clears: The gateway cron patch schema allows fallbacks to be an array or null, and mergeCronPayload deletes stored fallbacks when the patch value is null. (packages/gateway-protocol/src/schema/cron.ts:283, 41bea62b4a28)
• This PR duplicates the earlier narrow fix path: Live PR metadata shows this branch changes only src/agents/tools/cron-tool.ts and src/agents/tools/cron-tool.schema.test.ts with the same central fallback-parameterization fix that fix(cron): accept null fallbacks in update patch payload (#100707) #100801 already targets. (src/agents/tools/cron-tool.ts:318, 0c9e8ccc1584)
• Canonical PR is proof-positive and viable: The earlier PR is open, mergeable, labeled proof: sufficient and status: 👀 ready for maintainer look, and its body includes before/after terminal schema-validation proof for the same patch.payload.fallbacks: null gate. (a3b7a2b6125c)
• This branch still has prompt snapshot drift: The PR's CI reported prompt:snapshots:check drift for six Codex prompt snapshot fixtures after the tool schema changed, so this branch is not the best landing candidate as submitted. (package.json:1728, 0c9e8ccc1584)
• Feature history points to the cron tool schema and fallback-clear owners: History shows PR fix(cron-tool): add typed properties to job/patch schemas #55043 introduced the typed cron tool schema surface, PR fix(cron): expose per-job fallbacks in CLI #93369 added shipped fallback-clear behavior, and PR fix(cron): remove OpenAPI 3.0 incompatible JSON Schema keywords from cron tool #61221 recently maintained provider-compatible cron tool schemas. (src/agents/tools/cron-tool.ts:112, ca76e2fedc8e)

Likely related people:

• brunolorente: PR fix(cron-tool): add typed properties to job/patch schemas #55043 added the typed cron job and patch schema properties and adjacent schema tests that this bug exercises. (role: introduced typed cron tool schema surface; confidence: high; commits: ca76e2fedc8e, 3b9837e929b7, 42c59724f8d9; files: src/agents/tools/cron-tool.ts, src/agents/tools/cron-tool.schema.test.ts)
• 849261680: PR fix(cron): expose per-job fallbacks in CLI #93369 added the shipped CLI/API per-job fallback clear behavior that the tool schema now needs to expose. (role: recent cron fallback contributor; confidence: high; commits: 1662b07810eb, 4d085807c845; files: src/cli/cron-cli/register.cron-edit.ts, src/cron/service/jobs.ts, packages/gateway-protocol/src/schema/cron.ts)
• openperf: PR fix(cron): remove OpenAPI 3.0 incompatible JSON Schema keywords from cron tool #61221 recently adjusted the same cron tool schema and schema tests for provider-compatible JSON Schema output. (role: recent cron tool schema contributor; confidence: medium; commits: 8c1ca1f24517, 0eea926a3df6; files: src/agents/tools/cron-tool.ts, src/agents/tools/cron-tool.schema.test.ts)
• vincentkoc: Live PR metadata shows vincentkoc merged the recent provider-compatible cron schema PR, and git history shows release and adjacent cron touches in the same area. (role: recent reviewer/merger and release-adjacent contributor; confidence: medium; commits: 8c1ca1f24517, e085fa1a3ffd; files: src/agents/tools/cron-tool.ts, src/agents/tools/cron-tool.schema.test.ts)

Codex review notes: model internal, reasoning high; reviewed against 41bea62b4a28.