Best possible solution:

Keep the current runtime fallback and land this focused memory-slot regression coverage after the branch is rebased and normal maintainer review passes.

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

Yes. The PR creates a deterministic unit path where memory_search is a cataloged core ID that disappears when plugin tools are disabled, then verifies /tools/invoke retries with plugin tools enabled.

Is this the best way to solve the issue?

Yes for the patch content. Because the production fallback already exists on main, targeted regression coverage is the narrowest maintainable change; the remaining issue is mergeability, not design.

Acceptance criteria:

• Rebase the PR onto current main, then run the targeted gateway test for src/gateway/tools-invoke-http.test.ts and the relevant core test/type lanes.
• Confirm the PR remains test-only or explain any conflict-resolution runtime changes before merge.

What I checked:

• Current main fallback: invokeGatewayTool first resolves known core tool IDs with plugin tools disabled, then retries with plugin tools enabled if that known core tool is absent. (src/gateway/tools-invoke-shared.ts:212, a4c1c28a1731)
• Memory tools are cataloged core IDs: memory_search and memory_get are both listed in the core tool catalog, so they exercise the known-core fallback path when implemented by a plugin slot. (src/agents/tool-catalog.ts:129, a4c1c28a1731)
• Current main coverage shape: Current main has a generic plugin-backed catalog fallback test using browser, but no memory-specific fallback test in src/gateway/tools-invoke-http.test.ts. (src/gateway/tools-invoke-http.test.ts:938, a4c1c28a1731)
• PR diff scope: The PR modifies only src/gateway/tools-invoke-http.test.ts, adding mocked memory tools, recording tool creation contexts, and asserting [true, false] fallback for memory_search. (src/gateway/tools-invoke-http.test.ts:462, b167c63bb524)
• Head checks: Public check-runs for the exact PR head include successful node, build, lint/policy, and security checks, with CodeQL neutral and no retrieved failing check. (b167c63bb524)
• Mergeability: The live PR API reports mergeable: false and mergeable_state: dirty against the current base, so it needs a rebase or conflict resolution before normal merge. (b167c63bb524)

Likely related people:

• @ai-hpc: Merged PR feat(gateway): add SDK-facing tools.invoke RPC #74804 added the shared invokeGatewayTool path and SDK-facing tools.invoke surface that this PR covers with memory-specific regression tests. (role: introduced current shared Gateway tool-invoke implementation; confidence: high; commits: ef0eb126159f; files: src/gateway/tools-invoke-shared.ts, src/gateway/server-methods/tools-invoke.ts, src/gateway/tools-invoke-http.test.ts)
• @steipete: Recent history shows maintenance on the gateway test harness, plugin-backed catalog tool fallback, and tool catalog surfaces involved here. (role: recent gateway/tool-policy maintainer; confidence: medium; commits: 98a99765af18, 161b72230387, c4e5ca862517; files: src/gateway/tools-invoke-http.test.ts, src/gateway/tools-invoke-shared.ts, src/agents/tool-catalog.ts)
• @BunsDev: Recent commit history on tools-invoke-shared.ts includes fix(gateway): keep requested plugin tools invokable #76285 for keeping directly requested plugin tools invokable under restrictive profiles, adjacent to the fallback behavior covered by this PR. (role: recent adjacent owner; confidence: medium; commits: 57d6e63f30bc; files: src/gateway/tools-invoke-shared.ts, src/gateway/tool-resolution.ts, src/gateway/tools-invoke-http.test.ts)

Remaining risk / open question:

• The PR head is currently dirty against main, so the final diff and CI result may change after rebase.

Codex review notes: model gpt-5.5, reasoning high; reviewed against a4c1c28a1731.