simstudioai · waleedlatif1 · Aug 14, 2026 · Aug 14, 2026 · Aug 14, 2026
diff --git a/apps/sim/blocks/blocks/agent.ts b/apps/sim/blocks/blocks/agent.ts
@@ -6,6 +6,7 @@ import {
   getModelCapabilityCondition,
   getModelOptions,
   getProviderCredentialSubBlocks,
+  getSerializedModelProviderId,
   normalizeFileInput,
   RESPONSE_FORMAT_WAND_CONFIG,
 } from '@/blocks/utils'
@@ -29,6 +30,9 @@ import { useSubBlockStore } from '@/stores/workflows/subblock/store'
 import type { ToolResponse } from '@/tools/types'
 
 const logger = createLogger('AgentBlock')
+
+/** Model the agent block falls back to when `model` is unset or the auto pseudo-model. */
+const AGENT_FALLBACK_MODEL = 'claude-sonnet-5'
 const MODELS_WITH_REASONING_EFFORT = getModelsWithReasoningEffort()
 const MODELS_WITH_VERBOSITY = getModelsWithVerbosity()
 const MODELS_WITH_THINKING = getModelsWithThinking()
@@ -521,21 +525,10 @@ Return ONLY the JSON array.`,
     ],
     config: {
       tool: (params: Record<string, any>) => {
-        const model = params.model || 'claude-sonnet-5'
-        if (!model) {
-          throw new Error('No model selected')
-        }
-        // sim-auto resolves to a concrete pool model at execution time, where
-        // the agent handler derives the provider from the resolved model and
-        // never reads this serialized value. Serialization still needs the
-        // same provider-id shape every other model stores, so look up the
-        // runtime fallback model's provider.
-        const lookupModel = isAutoModel(model) ? 'claude-sonnet-5' : model
-        const tool = getBaseModelProviders()[lookupModel]
-        if (!tool) {
-          throw new Error(`Invalid model selected: ${model}`)
-        }
-        return tool
+        const model = params.model || AGENT_FALLBACK_MODEL
+        // sim-auto has no provider of its own until the pool resolves it at execution time.
+        const lookupModel = isAutoModel(model) ? AGENT_FALLBACK_MODEL : model
+        return getSerializedModelProviderId(lookupModel, AGENT_FALLBACK_MODEL)
       },
       params: (params: Record<string, any>) => {
         const normalizedFiles = normalizeFileInput(params.files)

diff --git a/apps/sim/blocks/blocks/evaluator.ts b/apps/sim/blocks/blocks/evaluator.ts
@@ -4,10 +4,9 @@ import type { BlockConfig, ParamType } from '@/blocks/types'
 import {
   getModelOptions,
   getProviderCredentialSubBlocks,
+  getSerializedModelProviderId,
   PROVIDER_CREDENTIAL_INPUTS,
 } from '@/blocks/utils'
-import { getBaseModelProviders } from '@/providers/models'
-import type { ProviderId } from '@/providers/types'
 import type { ToolResponse } from '@/tools/types'
 
 const logger = createLogger('EvaluatorBlock')
@@ -253,17 +252,7 @@ export const EvaluatorBlock: BlockConfig<EvaluatorResponse> = {
       'deepseek_reasoner',
     ],
     config: {
-      tool: (params: Record<string, any>) => {
-        const model = params.model || 'gpt-4o'
-        if (!model) {
-          throw new Error('No model selected')
-        }
-        const tool = getBaseModelProviders()[model as ProviderId]
-        if (!tool) {
-          throw new Error(`Invalid model selected: ${model}`)
-        }
-        return tool
-      },
+      tool: (params: Record<string, any>) => getSerializedModelProviderId(params.model),
     },
   },
   inputs: {

diff --git a/apps/sim/blocks/blocks/router.ts b/apps/sim/blocks/blocks/router.ts
@@ -3,10 +3,9 @@ import { AuthMode, type BlockConfig } from '@/blocks/types'
 import {
   getModelOptions,
   getProviderCredentialSubBlocks,
+  getSerializedModelProviderId,
   PROVIDER_CREDENTIAL_INPUTS,
 } from '@/blocks/utils'
-import { getBaseModelProviders } from '@/providers/models'
-import type { ProviderId } from '@/providers/types'
 import type { ToolResponse } from '@/tools/types'
 
 interface RouterResponse extends ToolResponse {
@@ -215,17 +214,7 @@ export const RouterBlock: BlockConfig<RouterResponse> = {
       'deepseek_reasoner',
     ],
     config: {
-      tool: (params: Record<string, any>) => {
-        const model = params.model || 'gpt-4o'
-        if (!model) {
-          throw new Error('No model selected')
-        }
-        const tool = getBaseModelProviders()[model as ProviderId]
-        if (!tool) {
-          throw new Error(`Invalid model selected: ${model}`)
-        }
-        return tool
-      },
+      tool: (params: Record<string, any>) => getSerializedModelProviderId(params.model),
     },
   },
   inputs: {
@@ -325,17 +314,7 @@ export const RouterV2Block: BlockConfig<RouterV2Response> = {
       'deepseek_reasoner',
     ],
     config: {
-      tool: (params: Record<string, any>) => {
-        const model = params.model || 'gpt-4o'
-        if (!model) {
-          throw new Error('No model selected')
-        }
-        const tool = getBaseModelProviders()[model as ProviderId]
-        if (!tool) {
-          throw new Error(`Invalid model selected: ${model}`)
-        }
-        return tool
-      },
+      tool: (params: Record<string, any>) => getSerializedModelProviderId(params.model),
     },
   },
   inputs: {

diff --git a/apps/sim/blocks/utils.test.ts b/apps/sim/blocks/utils.test.ts
@@ -72,11 +72,13 @@ import {
   BUILT_IN_TOOL_TYPES,
   getApiKeyCondition,
   getDependsOnFields,
+  getSerializedModelProviderId,
   getSubBlocksDependingOnChange,
   parseOptionalBooleanInput,
   parseOptionalJsonInput,
   parseOptionalNumberInput,
 } from '@/blocks/utils'
+import { getProviderFromModel } from '@/providers/utils'
 
 describe('BUILT_IN_TOOL_TYPES', () => {
   it('classifies the current File block instead of the legacy File block', () => {
@@ -464,3 +466,46 @@ describe('getSubBlocksDependingOnChange', () => {
     ).toEqual(['projectId'])
   })
 })
+
+describe('getSerializedModelProviderId', () => {
+  const resolver = vi.mocked(getProviderFromModel)
+
+  beforeEach(() => {
+    resolver.mockReset()
+    resolver.mockImplementation(((model: string) => {
+      if (model.startsWith('openrouter/')) return 'openrouter'
+      if (model === 'gpt-4o') return 'openai'
+      if (model === 'claude-sonnet-5') return 'anthropic'
+      throw new Error(`No provider found for model: ${model}`)
+    }) as unknown as typeof getProviderFromModel)
+  })
+
+  it('resolves a gateway model that the base model map deliberately omits', () => {
+    expect(getSerializedModelProviderId('openrouter/meta-llama/llama-4-maverick')).toBe(
+      'openrouter'
+    )
+  })
+
+  it('uses the fallback model when the model is still an unresolved reference', () => {
+    expect(getSerializedModelProviderId('openrouter/<variable.vllm>')).toBe('openai')
+    expect(resolver).not.toHaveBeenCalledWith('openrouter/<variable.vllm>')
+  })
+
+  it('honours a caller-supplied fallback model', () => {
+    expect(getSerializedModelProviderId(undefined, 'claude-sonnet-5')).toBe('anthropic')
+  })
+
+  it('never throws when the resolver rejects the model', () => {
+    expect(() => getSerializedModelProviderId('totally-unknown-model')).not.toThrow()
+    expect(getSerializedModelProviderId('totally-unknown-model')).toBe('openai')
+  })
+
+  it('never throws when the resolver rejects every model, including the fallback', () => {
+    resolver.mockImplementation((() => {
+      throw new Error('Provider "openai" is not available')
+    }) as unknown as typeof getProviderFromModel)
+
+    expect(() => getSerializedModelProviderId('gpt-4o')).not.toThrow()
+    expect(getSerializedModelProviderId('gpt-4o')).toBe('openai')
+  })
+})
diff --git a/apps/sim/blocks/utils.ts b/apps/sim/blocks/utils.ts
@@ -21,6 +21,7 @@ import {
   SIM_AUTO_MODEL_ID,
 } from '@/providers/models'
 import { isPiSupportedModel } from '@/providers/pi-providers'
+import type { ProviderId } from '@/providers/types'
 import { getProviderFromModel } from '@/providers/utils'
 import { useProvidersStore } from '@/stores/providers/store'
 
@@ -236,6 +237,45 @@ function shouldRequireApiKeyForModel(model: string): boolean {
   return true
 }
 
+/** Model whose provider is recorded when a block's own `model` cannot be resolved. */
+const SERIALIZATION_FALLBACK_MODEL = 'gpt-4o'
+
+/** Last-resort provider for when even {@link SERIALIZATION_FALLBACK_MODEL} cannot be resolved. */
+const SERIALIZATION_FALLBACK_PROVIDER: ProviderId = 'openai'
+
+/**
+ * Provider id a model-driven block records for `model` during serialization.
+ *
+ * Serialization runs before variable resolution, and every model block's handler
+ * re-derives the provider from the *resolved* model without ever reading this
+ * value — so it only has to be shape-correct, and it must never throw. Two cases
+ * reach here that {@link getBaseModelProviders} cannot answer: `model` may still
+ * hold a `<variable.x>` reference, and gateway providers (OpenRouter, vLLM,
+ * LiteLLM, Ollama, …) are deliberately absent from that map even when the model
+ * id is perfectly valid. A reference resolves to {@link SERIALIZATION_FALLBACK_MODEL}'s
+ * provider; anything else is left to `getProviderFromModel`, which defaults an
+ * unrecognised id to `ollama` rather than failing serialization with an error the
+ * user cannot act on.
+ *
+ * The remaining throw is a blacklisted provider or model, which is env-driven and
+ * can name the fallback itself — so recovery returns
+ * {@link SERIALIZATION_FALLBACK_PROVIDER} outright rather than resolving a second
+ * time through the function that just threw.
+ */
+export function getSerializedModelProviderId(
+  model: unknown,
+  fallbackModel: string = SERIALIZATION_FALLBACK_MODEL
+): ProviderId {
+  const candidate =
+    typeof model === 'string' && model && !containsReference(model) ? model : fallbackModel
+
+  try {
+    return getProviderFromModel(candidate)
+  } catch {
+    return SERIALIZATION_FALLBACK_PROVIDER
+  }
+}
+
 /**
  * Visibility condition for a model-tuning field that only some models accept, such as
  * reasoning effort or verbosity. Gates on the capability list, but keeps the field visible

diff --git a/apps/sim/providers/utils.test.ts b/apps/sim/providers/utils.test.ts
@@ -948,6 +948,15 @@ describe('Provider Management', () => {
       expect(getProviderFromModel('unknown-model')).toBe('ollama')
     })
 
+    it('should resolve gateway models that getBaseModelProviders deliberately omits', () => {
+      // getBaseModelProviders() filters these providers out entirely, so a model
+      // block that looked models up there rejected valid ids like these.
+      expect(getProviderFromModel('openrouter/meta-llama/llama-4-maverick')).toBe('openrouter')
+      expect(getProviderFromModel('together/some-model')).toBe('together')
+      expect(getProviderFromModel('fireworks/some-model')).toBe('fireworks')
+      expect(getBaseModelProviders()['openrouter/meta-llama/llama-4-maverick']).toBeUndefined()
+    })
+
     it('should be case insensitive', () => {
       expect(getProviderFromModel('GPT-4O')).toBe('openai')
       expect(getProviderFromModel('CLAUDE-SONNET-4-0')).toBe('anthropic')

diff --git a/packages/logger/src/index.test.ts b/packages/logger/src/index.test.ts
@@ -263,6 +263,46 @@ describe('Logger', () => {
       expect(parsed.self.self).toBe('[Circular]')
     })
 
+    test('should render an Error held under a key as its message, not {}', () => {
+      const error = new Error('boom')
+
+      createEnabledLogger().error('failed', { error })
+
+      const parsed = JSON.parse(consoleErrorSpy.mock.calls[0][0] as string)
+      expect(parsed.error).toBe('boom')
+      expect(parsed.stack).toBe(error.stack)
+    })
+
+    test('should render an Error under a non-conventional key without hijacking stack', () => {
+      createEnabledLogger().error('failed', { cause: new Error('inner'), stack: 'caller-supplied' })
+
+      const parsed = JSON.parse(consoleErrorSpy.mock.calls[0][0] as string)
+      expect(parsed.cause).toBe('inner')
+      expect(parsed.stack).toBe('caller-supplied')
+    })
+
+    test('should keep sibling keys alongside an Error value', () => {
+      createEnabledLogger().error('failed', { error: new Error('boom'), toolId: 'slack_message' })
+
+      const parsed = JSON.parse(consoleErrorSpy.mock.calls[0][0] as string)
+      expect(parsed.error).toBe('boom')
+      expect(parsed.toolId).toBe('slack_message')
+    })
+
+    test('should unwrap an Error held under a key on the colorized path too', () => {
+      const colorized = new Logger('Test', {
+        enabled: true,
+        colorize: true,
+        logLevel: LogLevel.DEBUG,
+      })
+
+      colorized.error('failed', { error: new Error('boom') })
+
+      const printed = consoleErrorSpy.mock.calls[0].join(' ')
+      expect(printed).toContain('boom')
+      expect(printed).not.toContain('"error":{}')
+    })
+
     test('should emit a line instead of throwing on BigInt metadata', () => {
       expect(() => createEnabledLogger().error('boom', { size: 10n })).not.toThrow()
       expect(consoleErrorSpy).toHaveBeenCalledTimes(1)

diff --git a/packages/logger/src/index.ts b/packages/logger/src/index.ts
@@ -130,39 +130,85 @@ const getLogConfig = () => {
   }
 }
 
+/**
+ * Renders an error as the plain object `JSON.stringify` cannot produce for it.
+ *
+ * `message`, `stack` and `name` are non-enumerable on `Error.prototype`, so a
+ * plain stringify emits `{}`. Own enumerable properties are copied too — driver
+ * and HTTP errors carry the useful part (`code`, `status`) there.
+ */
+const errorToPlainObject = (error: Error, isDev: boolean): Record<string, unknown> => {
+  const errorObj: Record<string, unknown> = {
+    message: error.message,
+    stack: isDev ? error.stack : undefined,
+    name: error.name,
+  }
+  for (const key of Object.keys(error)) {
+    if (!(key in errorObj)) {
+      errorObj[key] = (error as unknown as Record<string, unknown>)[key]
+    }
+  }
+  return errorObj
+}
+
 /**
  * Format objects for logging
+ *
+ * Errors held under a key are unwrapped as well as bare ones — `{ error }` is
+ * the common call shape, and it would otherwise print as `{"error":{}}`.
  */
 const formatObject = (obj: unknown, isDev: boolean): string => {
   try {
     if (obj instanceof Error) {
-      const errorObj: Record<string, unknown> = {
-        message: obj.message,
-        stack: isDev ? obj.stack : undefined,
-        name: obj.name,
+      return JSON.stringify(errorToPlainObject(obj, isDev), null, isDev ? 2 : 0)
+    }
+    if (obj && typeof obj === 'object' && !Array.isArray(obj)) {
+      let unwrapped: Record<string, unknown> | undefined
+      for (const [key, value] of Object.entries(obj as Record<string, unknown>)) {
+        if (!(value instanceof Error)) continue
+        unwrapped ??= { ...(obj as Record<string, unknown>) }
+        unwrapped[key] = errorToPlainObject(value, isDev)
       }
-      for (const key of Object.keys(obj)) {
-        if (!(key in errorObj)) {
-          errorObj[key] = (obj as unknown as Record<string, unknown>)[key]
-        }
+      if (unwrapped) {
+        return JSON.stringify(unwrapped, null, isDev ? 2 : 0)
       }
-      return JSON.stringify(errorObj, null, isDev ? 2 : 0)
     }
     return JSON.stringify(obj, null, isDev ? 2 : 0)
   } catch {
     return '[Circular or Non-Serializable Object]'
   }
 }
 
-/** Merges caller-supplied log arguments into the structured entry. */
+/**
+ * Merges caller-supplied log arguments into the structured entry.
+ *
+ * `Error.message` and `Error.stack` are non-enumerable, so `JSON.stringify`
+ * renders an error held under a key as `{}` — and `logger.x('...', { error })`
+ * is by far the most common call shape, which would otherwise reduce the one
+ * field worth reading to an empty object. Errors nested in an object argument
+ * are therefore unwrapped like a bare `Error` argument. `error` stays a plain
+ * message string so log queries can group on it; richer diagnostics are opt-in
+ * via `describeError` from `@sim/utils/errors`.
+ */
 const mergeArgs = (entry: Record<string, unknown>, args: unknown[]): Record<string, unknown> => {
   for (const arg of args) {
     if (arg === null || arg === undefined) continue
     if (arg instanceof Error) {
       entry.error = arg.message
       entry.stack = arg.stack
     } else if (typeof arg === 'object') {
-      Object.assign(entry, arg)
+      const source = arg as Record<string, unknown>
+      for (const key of Object.keys(source)) {
+        const value = source[key]
+        if (value instanceof Error) {
+          entry[key] = value.message
+          if (key === 'error' && entry.stack === undefined) {
+            entry.stack = value.stack
+          }
+        } else {
+          entry[key] = value
+        }
+      }
     } else {
       entry.extra = arg
     }