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fix(harness): retarget request.model on fallback; report a model switch once - #325
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Add tests asserting that an applied switch reports exactly one accepted outcome across model calls, that rejected switches report only the rejection, and that fallback after a steered or middleware-pinned model retargets the request model to the fallback. Also tighten an existing steering test to assert that queuing a switch emits no outcome event, since the agent loop reports it only at the model-call boundary. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
The fallback test now passes an empty context and a RunConfig to invoke, matching the updated harness API. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
A queued SwitchModel no longer emits a Steered event at the checkpoint; its single outcome is reported when the model call applies it (accepted: true) or rejects it (accepted: false), so a switch the second validation pass rejects is never announced as accepted first. The fallback chain now retargets the request's wire-level model override on every rebinding, so a fallback no longer re-asks the model that just failed while events report the fallback's name. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
Clarify that a queued model switch produces exactly one outcome, emitted when the model call first applies or rejects it, and that a switch replaced or ended before any model call is never reported. Also note that each fallback call's request.model is retargeted to the fallback's own name so adapters never re-ask the model that just failed. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
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📝 WalkthroughWalkthroughModel-switch outcomes are reported when the model call applies or rejects a switch. Fallback attempts now receive requests whose ChangesModel invocation behavior
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix Merge Risk: 🔵 Low · up to A switch can be reported as accepted even though no model call occurs. This is a bounded reporting error that should be corrected, but it does not prevent merging. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The changes align fallback requests with the configured destination while preserving selection and eligibility checks. No new security weakness was established in the inspected paths, but incomplete coverage limits end-to-end assurance. Retained concerns Security review detailsSecurity Blast Radius
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Tiny Sweeper reviewTiny Sweeper reviewed this change across 6 lane(s) and found 0 active actionable finding(s), 15 resolved finding(s) across the history. Detailed lane evidence and any incomplete work are listed below. State: Changes requested Review snapshot
Completeness: Complete What changedTwo coordinated fixes in the agent loop's model-call and steering surfaces. First, wire-level retargeting: each attempt's `ModelRequest` is cloned before the fallback walk and its `request.model` is re-pointed at whichever binding is about to be called, so a provider adapter that honours `request.model` asks for the fallback binding rather than re-asking the model that just failed. The retargeting is conditional: only requests that already carried an explicit model are re-pointed; a request that sent none (relying on the provider's own configured model) keeps sending none, because registry names are runtime aliases and not guaranteed provider model ids. Second, one-outcome reporting for steered model switches: a queued switch no longer emits a `Steered` event at the queuing checkpoint; the single `Steered { accepted: true }` is emitted once when the model call actually dispatches the request carrying the switched model, or the `accepted: false` rejection is emitted when the switch is rejected. A switch superseded before it was reported now emits an explicit `accepted: false` for the superseded command, and a switch replaced after it was reported, or whose run ends before validation, emits no additional outcome. The applied-reporting is claimed via a per-handle flag reset by every new switch; the flag claim happens under the same lock that guards the override slot, and the base model call claims the switch only after the wrap middleware onion elects to call that base, so a wrap middleware that short-circuits with a replacement response produces no switch outcome. The steering README documents the one-outcome contract and the fallback retargeting. Features
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How this fits togetherflowchart LR
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Review comments at @crates/tinyagents-harness/src/agent_loop/model_switch.rs:
- Around line 97-104: Move the `Steered` event emission out of the final
switch-pass handling and into the model-dispatch path, so `accepted: true` is
emitted only when a model call is actually dispatched. Use
`handle.announce_model_override()` to preserve the existing condition, and avoid
emitting acceptance when pending controls, including `JumpTo(End)`, prevent
dispatch.
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crates/tinyagents-harness/src/agent_loop/model_call.rscrates/tinyagents-harness/src/agent_loop/model_switch.rscrates/tinyagents-harness/src/agent_loop/model_switch_tests.rscrates/tinyagents-harness/src/agent_loop/run_loop.rscrates/tinyagents-harness/src/steering/README.mdcrates/tinyagents-harness/src/steering/mod.rscrates/tinyagents-harness/src/steering/mod_tests.rscrates/tinyagents-harness/src/steering/types.rs
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Requesting changes: 1 lane(s) blocking, worst finding is critical.
Fix or reply to the findings below and push. The next review clears this automatically once they are gone — you should not need to dismiss anything by hand.
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description: $0.0001 · 8,672 in / 197 out · 1,536 cached (18%) · glm-5.3-flash
Fallback attempts now only rewrite the wire-level request model when the request already carried an explicit model, since registry names are runtime aliases rather than guaranteed provider model ids. The redundant final-pass model override announcement was also dropped. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
…rtain The applied-switch event was emitted during the final validation pass, before the request was guaranteed to be dispatched, so a switch could be reported as accepted even when a later control effect exited the turn. The announcement now happens after the control checkpoint, and the override is only reported when it still matches the model actually being applied. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
Add a helper that reports a steered model switch as applied once the request carrying the switched model is about to be dispatched. It runs after the pre-call control checkpoint so switches whose request never reaches a model call produce no outcome. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
Add tests for two model-switch edge cases: a switch whose call is cancelled by a before_model_control hook that jumps to the end of the loop, which should report no switch outcome, and a failover fallback where the original request had no model set, which should stay absent rather than inventing a provider model id from the registry alias. Auto-committed-on: dragonfly Co-authored-by: Medulla <medulla@tinyhumans.ai>
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The previously-blocking findings are resolved. Clearing the changes request.
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description: $0.0001 · 9,927 in / 791 out · 0 cached (0%) · glm-5.3-flash
Co-authored-by: Medulla <medulla@tinyhumans.ai>
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Requesting changes: 1 lane(s) blocking, worst finding is high.
Fix or reply to the findings below and push. The next review clears this automatically once they are gone — you should not need to dismiss anything by hand.
$0.0112 · 231,584 in / 13,232 out · 15,831 cached (7%) · gpt-5.6-luna, glm-5.3-flash
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| /// but only when the request already carried an explicit model. Registry names | ||
| /// are runtime aliases, not guaranteed provider model ids, so a request that | ||
| /// sent none (the provider's own configured model) keeps sending none. | ||
| fn retarget_request_model(request: &mut ModelRequest, name: &str) { |
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Retarget fallbacks with provider model identifiers
name is the resolved registry name, not necessarily the model identifier accepted by the provider. For example, an explicit request for a provider ID resolved through registry entry primary can fall back to registry entry backup; this changes the request to model = "backup", and the fallback adapter may reject it or invoke the wrong model. The comment acknowledges that registry names are not guaranteed provider IDs, but the function still writes them onto the wire request. Use the fallback binding's provider-facing identifier (or an API that explicitly guarantees registry names are valid overrides) instead of blindly copying the registry name.
[RULE] invalid-wire-identifier ·
ignroe
Follow-up to #324 (opt-in
SwitchModelsteering), addressing its two Codex threads.P1 -- stale
request.modelafter fallback (confirmed bug)ClaudeCodeProviderandClaudeAgentSdkProviderreadrequest.modelas the CLI model override.invoke_model_resolvingreboundmodel/current_nameon fallback but kept sending the original request, so the fallback binding could be called with the failed model's name. This was pre-existing for anyrequest.modeloverride (SDK caller orbefore_modelmiddleware), not just steering.Fix:
invoke_model_resolvingnow sends a per-attempt request whosemodelis retargeted to the fallback's name at every rebinding (the written-off-model skip, in-chain fallback and chain-head fallback), for both unary and streaming calls.Tests: fallback from a steered model in the chain, chain-head fallback for a steered model outside the chain, and a plain middleware
request.modeloverride that fails over; each asserts the fallback's recordedrequest.modelis its own name.P2 -- one command reported as accepted and rejected (confirmed)
The checkpoint emitted
Steered { accepted: true }on queueing, then the model call could emitaccepted: false.Fix: queuing a switch emits nothing. The model-call boundary reports the single outcome:
accepted: trueonce, on the final (post-before_model) application, tracked by an announced flag on the run-local steering state so a sticky switch is not re-announced each call;accepted: falseon rejection. A switch rejected only after middleware raised the capability requirements is therefore never reported accepted first. Blank-name and policy rejections are unchanged. A switch replaced or never reached by a model call is not reported (documented in the steering README).Tests: applied switch across two calls yields exactly
[true]; rejected switch yields[false]; rejected-after-middleware yields[false]; the checkpoint unit test now asserts noSteeredfor a queued switch.Checks
cargo test -p tinyagents-harness: 2078 pass; the only failure is the pre-existingworkspace::git::validate_repo_root_rejects_non_repo(/tmp-related). clippy-D warningsclean with and without--all-features; rustfmt clean on changed files.cargo doc -D warningsreports only intra-doc link errors that already exist on main (lib.rs, phases.rs, private-item links in steering/types.rs and mod.rs).Co-authored-by: Medulla medulla@tinyhumans.ai
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