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kandev/docs/specs/agents/system-design/no-silent-model-fallback-02.md
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current agents
REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001
REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-003
2026-08-23
kandev

No Silent Model Fallback System Design Part 2

Purpose and boundaries

This design records risks for executor-authoritative model fallback and unique variation resolution.

Requirement mapping

Requirement Design section
REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001 Migrated source detail
REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002 Risks & Open Questions
REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-003 Risks & Open Questions

Migrated source detail

Risks & Open Questions

  • Behavior change for existing profiles: an unadvertised start model no longer stops the launch. Kandev uses the executor agent default and persists an actionable warning.
  • Office post-start fallback remains workspace-routing-governed: a default-mode profile's Office run can still be re-dispatched to another provider mid-session by the ADR office policy (availability codes → DecisionFallback). This is intentional — office authorization is the workspace routing configuration, not the execution profile — and is documented in the behavior matrix above.
  • Probe staleness: the advertised list can be stale (probe cached). The profile editor uses it only as a hint. Profile selectors do not render host model advisories. The executor session catalog owns the launch decision.
  • Cold Claude model lists: a valid restricted model can be absent from a cold bridge's initial list. Pre-session exposure lets the bridge include and select the configured model. If the bridge still omits it, Kandev uses the agent default and persists a warning.
  • Context reset model changes: this amendment covers the model selected before the initial process starts. It does not restart a live ACP bridge to expose a newly selected hidden model during context reset.
  • Office vs. kanban surfaces: both share the same agent-profile rows. The shared selector behavior covers kanban task creation and Office setup. Office run-detail routing surfaces are unchanged.
  • Collapsed controls remain legible: the disclosure header summarizes the effective mode, and dirty-state decoration is applied to the disclosure container so a collapsed section cannot conceal that it has unsaved changes.
  • Hover is supplementary: every info icon is focusable, and coarse-pointer devices receive the same content in a drawer. The visible option helper copy remains the baseline explanation.
  • Provider-specific labels remain opaque: 1m, 270k, and fast have no Kandev-defined order. More than one variation therefore fails closed to the existing provider-default path.
  • Host and executor decisions can differ: a unique host variation is only an advisory. The selected executor can advertise zero, one, or multiple variations at launch.
  • Bracketed requests do not drift sideways: a request such as opus[1m] does not infer opus[270k]. The user must select another explicit model.
  • Legacy automatic fallback remains unchanged: when auto_fallback is enabled and the requested model is absent, Kandev does not apply an explicit fallback or infer a variation. It continues with the provider default.
  • Removal must be narrow: authentication, missing-CLI, and failed-probe indicators remain. Profile-editor advisories and persisted task warnings retain their existing behavior.
  • Evidence has limits: a model warning does not prove a cache defect. Discovery refresh or normalization changes require separate root-cause evidence; this amendment does not change those contracts.