Best possible solution:

Keep the doctor-only compatibility repair, align configured-channel detection with reserved channel metadata keys, then continue maintainer review with exact-head validation.

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

Yes. Source inspection shows current main defaults group/channel delivery to message-tool-only, while the current doctor compatibility chain has no path that persists messages.groupChat.visibleReplies for older configured-channel configs.

Is this the best way to solve the issue?

No, not quite. The doctor-only migration is the right maintainable surface, but the configured-channel check should ignore channels.modelByChannel so doctor does not mutate configs without real channel sections.

Full review comments:

• [P3] Ignore channel metadata when detecting configured channels — src/commands/doctor/shared/legacy-config-core-normalizers.ts:24
channels.modelByChannel is reserved channel metadata, not a configured channel block. With only that mapping present, this helper still adds messages.groupChat.visibleReplies, contradicting the no-channel case and causing doctor to churn channel-model-only configs; please exclude modelByChannel and cover it in the no-channel regression test.
  Confidence: 0.78

Overall correctness: patch is correct
Overall confidence: 0.82

Acceptance criteria:

• pnpm test src/commands/doctor-legacy-config.migrations.test.ts src/config/defaults.test.ts src/commands/setup.test.ts
• pnpm config:schema:check
• pnpm config:docs:check
• git diff --check
• pnpm check:changed

What I checked:

• Protected label: The provided GitHub context lists the maintainer label, so cleanup automation should not close this PR even if the proposed repair is useful. (d171bf15d1d2)
• Current group/channel default: Current main resolves group and channel source replies to message_tool_only unless messages.groupChat.visibleReplies or messages.visibleReplies is explicitly set to automatic. (src/auto-reply/reply/source-reply-delivery-mode.ts:28, e02377f52281)
• Doctor compatibility surface: Doctor runs normalizeCompatibilityConfigValues(candidate) during the config repair flow, so a compatibility normalizer is the narrow doctor-owned place to persist this default. (src/commands/doctor-config-flow.ts:140, e02377f52281)
• Current main lacks this normalizer: The current base compatibility chain has legacy message/config migrations but no step that writes messages.groupChat.visibleReplies for configured-channel configs. (src/commands/doctor/shared/legacy-config-compatibility-base.ts:39, e02377f52281)
• Reserved channel metadata contract: Current config schema code treats channels.modelByChannel as reserved metadata, not as a plugin-owned channel section. (src/config/zod-schema.providers.ts:44, e02377f52281)
• PR edge case: The PR helper shown in the provided diff excludes only defaults when deciding whether channels are configured, so a config with only channels.modelByChannel would still be mutated. (src/commands/doctor/shared/legacy-config-core-normalizers.ts:24, d171bf15d1d2)

Likely related people:

• scoootscooob: The related merged group/channel visible-reply behavior is credited to this contributor in fix(discord): make always-on auto replies more robust #73046, and local history contains commit 3c636208b0a0 for keeping group replies tool-only by default. (role: introduced behavior / domain contributor; confidence: high; commits: d8dc4eb180e6, 3c636208b0a0; files: src/auto-reply/reply/source-reply-delivery-mode.ts, src/config/types.messages.ts, docs/channels/groups.md)

Remaining risk / open question:

• Exact PR-head checks were not rerun in this read-only review; merge should still be gated on CI or the listed validation commands after the metadata edge is fixed.

Codex review notes: model gpt-5.5, reasoning high; reviewed against e02377f52281.