Summary

Closes #2339.

Removes the Pi-era per-message model override pathway (channel overrides + heartbeat override) that was wired into the reply pipeline but had no observable effect: ChannelBridge selects the CLI runtime via resolveAgentRuntimeOrThrow(cfg, agentId) and ChannelMessage (the bridge's input payload) has no model field. Override values were computed for UX notification / cli-session keying, but never changed agent execution.

Decision: Option B (gut)

Rationale: Per RemoteClaw's Middleware Boundary Principle — agents bring their own model selection; RemoteClaw provides channel routing and session management. The CLI runtime binding is an agent-level config decision, not a channel or message decision.

Option A (repair) was rejected: redefining semantics as per-channel runtime selection would need ChannelBridge to honor the override and would reintroduce complexity that was deliberately removed in the gutting waves.

Changes

Deleted

• src/channels/model-overrides.ts
• src/channels/model-overrides.test.ts
• src/infra/heartbeat-runner.model-override.test.ts

Schema removal

• channels.modelByChannel — types (types.channels.ts), zod (zod-schema.providers.ts), help/labels (schema.help.ts, schema.labels.ts), validation allowlist (validation.ts), doctor / plugin-auto-enable exclusion filters
• agents.defaults.heartbeat.model — types (types.agent-defaults.ts), zod (zod-schema.agent-runtime.ts)
• GetReplyOptions.heartbeatModelOverride (auto-reply/types.ts)
• HeartbeatSummary.model (consumer read the same gutted field)

Wiring removal

• get-reply.ts: heartbeat override block, channel override block (resolveChannelModelOverride consumption), hasResolvedHeartbeatModelOverride / hasSessionModelOverride locals, unused resolveModelRefFromString import
• get-reply-directives.ts: dead hasResolvedHeartbeatModelOverride type param (was declared but never read in the body)
• heartbeat-runner.ts: heartbeatModelOverride local + conditional replyOpts construction
• get-reply.test-mocks.ts: resolveChannelModelOverride mock

Tests updated

• config.plugin-validation.test.ts: removed modelByChannel from a validation test case
• plugin-auto-enable.test.ts: removed ignores channels.modelByChannel test (feature no longer exists)
• config.legacy-config-detection.accepts-imessage-dmpolicy.test.ts: swapped heartbeat.model in a legacy-config fixture for target (the test intent is to flag top-level heartbeat, not the model subfield)
• reply.triggers...native-stop.e2e.test.ts: removed the heartbeat-override model case; kept the stored-override (session /model) case

Docs

• docs/gateway/configuration-reference.md: removed "Channel model overrides" section
• docs/gateway/heartbeat.md: removed model field from config sample and field-notes list
• src/config/legacy.rules.ts: updated error message that enumerated heartbeat subfields

Left alone (verified separate paths, per issue guidance)

• sessionEntry.modelOverride / sessionEntry.providerOverride — session-level /model directive, unrelated to channel overrides; still live via /cron/isolated-agent/run.ts and directive-handling.fast-lane.ts
• onModelSelected callback — fires on any model selection (including fallback); not tied to channel overrides
• fallbackTransition state — tracks primary→fallback model transitions in agent-runner.ts; independent path

Follow-ups deferred to #2342, #2343, #2344, #2345 (ChannelBridge regressions tracked separately by #2089's audit).

Acceptance criteria

• Decision documented (Option B — gut) with rationale
• Files deleted / modified per gut: remove decoratively-wired Pi-era per-message model override flow #2339 scope
• pnpm check passes (format + tsgo + lint)
• pnpm test passes (721 files / 6323 tests)
• Verification grep: git grep -rn \"modelByChannel\\|heartbeatModelOverride\\|resolveChannelModelOverride\" src/ — zero hits
• Repo-wide grep (including docs) — zero hits

Test plan

• Full pnpm check green
• Full pnpm test green (no regressions)
• CI zombie-import gate (validated in PR CI)
• LIVE smoke tests for middleware/runtime (this PR touches src/auto-reply and src/infra/heartbeat-runner.ts — recommend running `LIVE=1 pnpm test:live` in the PR drive loop)

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