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feat: add customizable fallback chains and improved model matching (Fixes #1307) #1436

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feat: add customizable fallback chains and improved model matching (Fixes #1307) #1436

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07825f6
feat: add customizable fallback chains and improved model matching
wydrox Jan 31, 2026
37dcb73
fix: resolve conflicts and fix priority in agent-variant
wydrox Feb 3, 2026
ea9f70f
chore: update lockfile
wydrox Feb 3, 2026
31f2155
fix(agent-variant): require model match when entry.model is defined i…
wydrox Feb 3, 2026
c1125a3
test(agent-variant): add edge case tests for findVariantInChain logic
wydrox Feb 3, 2026
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28 changes: 14 additions & 14 deletions bun.lock
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11 changes: 11 additions & 0 deletions src/config/schema.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,13 @@ export const BuiltinCommandNameSchema = z.enum([
"start-work",
])

export const FallbackChainEntrySchema = z.object({
providers: z.array(z.string()),
model: z.string(),
variant: z.string().optional(),
})
export const FallbackChainSchema = z.array(FallbackChainEntrySchema)

export const AgentOverrideConfigSchema = z.object({
/** @deprecated Use `category` instead. Model is inherited from category defaults. */
model: z.string().optional(),
Expand Down Expand Up @@ -135,6 +142,8 @@ export const AgentOverrideConfigSchema = z.object({
textVerbosity: z.enum(["low", "medium", "high"]).optional(),
/** Provider-specific options. Passed directly to OpenCode SDK. */
providerOptions: z.record(z.string(), z.unknown()).optional(),
/** Custom fallback chain for model resolution. Overrides built-in agent fallback chains. */
fallback_chain: FallbackChainSchema.optional(),
})

export const AgentOverridesSchema = z.object({
Expand Down Expand Up @@ -189,6 +198,8 @@ export const CategoryConfigSchema = z.object({
prompt_append: z.string().optional(),
/** Mark agent as unstable - forces background mode for monitoring. Auto-enabled for gemini/minimax models. */
is_unstable_agent: z.boolean().optional(),
/** Custom fallback chain for model resolution. Each entry specifies providers, model, and optional variant. */
fallback_chain: FallbackChainSchema.optional(),
})

export const BuiltinCategoryNameSchema = z.enum([
Expand Down
197 changes: 197 additions & 0 deletions src/shared/agent-variant.test.ts
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Expand Up @@ -211,4 +211,201 @@ describe("resolveVariantForModel", () => {
// then
expect(variant).toBe("max")
})

test("matches model with antigravity- prefix to base model", () => {
// #given
const config = {} as OhMyOpenCodeConfig
const model = { providerID: "anthropic", modelID: "antigravity-claude-opus-4-5" }

// #when
const variant = resolveVariantForModel(config, "sisyphus", model)

// #then
expect(variant).toBe("max")
})

test("uses user-defined fallback_chain when provided for agent", () => {
// #given
const config = {
agents: {
sisyphus: {
fallback_chain: [
{ providers: ["custom-provider"], model: "custom-model", variant: "custom-variant" }
]
}
}
} as OhMyOpenCodeConfig
const model = { providerID: "custom-provider", modelID: "custom-model" }

// #when
const variant = resolveVariantForModel(config, "sisyphus", model)

// #then
expect(variant).toBe("custom-variant")
})

test("uses user-defined fallback_chain when provided for category", () => {
// #given
const config = {
agents: {
"custom-agent": { category: "my-category" }
},
categories: {
"my-category": {
model: "some/model",
fallback_chain: [
{ providers: ["google"], model: "gemini-3-pro", variant: "high" }
]
}
}
} as OhMyOpenCodeConfig
const model = { providerID: "google", modelID: "antigravity-gemini-3-pro" }

// #when
const variant = resolveVariantForModel(config, "custom-agent", model)

// #then
expect(variant).toBe("high")
})

test("falls back to agent variant when no fallback chain matches", () => {
// #given
const config = {
agents: {
"custom-agent": { variant: "fallback-variant" }
}
} as OhMyOpenCodeConfig
const model = { providerID: "unknown-provider", modelID: "unknown-model" }

// #when
const variant = resolveVariantForModel(config, "custom-agent", model)

// #then
expect(variant).toBe("fallback-variant")
})

test("falls back to category variant when no fallback chain matches", () => {
// #given
const config = {
agents: {
"custom-agent": { category: "my-category" }
},
categories: {
"my-category": {
model: "some/model",
variant: "category-fallback-variant"
}
}
} as OhMyOpenCodeConfig
const model = { providerID: "unknown-provider", modelID: "unknown-model" }

// #when
const variant = resolveVariantForModel(config, "custom-agent", model)

// #then
expect(variant).toBe("category-fallback-variant")
})

// Edge case tests for PR #1307 fix
test("does not select variant when provider matches but model does not", () => {
// given
const config = {
agents: {
testAgent: {
fallback_chain: [
{ providers: ["anthropic"], model: "claude-opus-4", variant: "max" }
]
}
}
} as OhMyOpenCodeConfig
const model = { providerID: "anthropic", modelID: "claude-sonnet-4" } // Different model

// when
const variant = resolveVariantForModel(config, "testAgent", model)

// then
expect(variant).toBeUndefined()
})

test("selects variant when provider matches and entry has no model", () => {
// given
const config = {
agents: {
testAgent: {
fallback_chain: [
{ providers: ["anthropic"], variant: "high" } // No model specified
]
}
}
} as OhMyOpenCodeConfig
const model = { providerID: "anthropic", modelID: "any-model" }

// when
const variant = resolveVariantForModel(config, "testAgent", model)

// then
expect(variant).toBe("high")
})

test("does not match when modelID is undefined but entry requires model", () => {
// given
const config = {
agents: {
testAgent: {
fallback_chain: [
{ providers: ["anthropic"], model: "claude-opus-4", variant: "max" }
]
}
}
} as OhMyOpenCodeConfig
const model = { providerID: "anthropic", modelID: undefined } as any // Forced undefined

// when
const variant = resolveVariantForModel(config, "testAgent", model)

// then
expect(variant).toBeUndefined()
})

test("skips mismatched entries and finds later matching entry", () => {
// given
const config = {
agents: {
testAgent: {
fallback_chain: [
{ providers: ["anthropic"], model: "claude-opus-4", variant: "max" }, // Wrong model
{ providers: ["anthropic"], model: "claude-sonnet-4", variant: "high" } // Correct
]
}
}
} as OhMyOpenCodeConfig
const model = { providerID: "anthropic", modelID: "claude-sonnet-4" }

// when
const variant = resolveVariantForModel(config, "testAgent", model)

// then
expect(variant).toBe("high")
})

test("respects model matching for entries with multiple providers", () => {
// given
const config = {
agents: {
testAgent: {
fallback_chain: [
{ providers: ["anthropic", "openai"], model: "gpt-4", variant: "high" }
]
}
}
} as OhMyOpenCodeConfig
// Provider matches (anthropic) but model (claude-opus-4) doesn't match gpt-4
const model = { providerID: "anthropic", modelID: "claude-opus-4" }

// when
const variant = resolveVariantForModel(config, "testAgent", model)

// then
expect(variant).toBeUndefined()
})
})
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