fix: OpenAI adapter tool calling compatibility

Two fixes for OpenAI-compatible provider compatibility:

1. Sanitize JSON Schema `const` → `enum` in tool parameters.
   Many OpenAI-compatible endpoints (Ollama, DeepSeek, vLLM, etc.)
   do not support the `const` keyword in JSON Schema. Recursively
   convert `const: value` to `enum: [value]` which is semantically
   equivalent.

2. Force stop_reason to `tool_use` when tool_calls are present.
   Some backends incorrectly return finish_reason "stop" even when
   the response contains tool_calls. Without this fix, the query
   loop treats the response as a normal end_turn and never executes
   the requested tools.

src/services/api/openai/__tests__/convertTools.test.ts

@@ -59,6 +59,88 @@ describe('anthropicToolsToOpenAI', () => {
   test('handles empty tools array', () => {
     expect(anthropicToolsToOpenAI([])).toEqual([])
   })
+
+  test('sanitizes const to enum in tool schema', () => {
+    const tools = [
+      {
+        type: 'custom',
+        name: 'test',
+        description: 'test tool',
+        input_schema: {
+          type: 'object',
+          properties: {
+            mode: { const: 'read' },
+            name: { type: 'string' },
+          },
+        },
+      },
+    ]
+    const result = anthropicToolsToOpenAI(tools as any)
+    const props = result[0].function.parameters as any
+    expect(props.properties.mode).toEqual({ enum: ['read'] })
+    expect(props.properties.mode.const).toBeUndefined()
+    expect(props.properties.name).toEqual({ type: 'string' })
+  })
+
+  test('sanitizes const in deeply nested schemas', () => {
+    const tools = [
+      {
+        type: 'custom',
+        name: 'deep',
+        description: 'nested const',
+        input_schema: {
+          type: 'object',
+          properties: {
+            outer: {
+              type: 'object',
+              properties: {
+                inner: { const: 'fixed' },
+              },
+            },
+          },
+          definitions: {
+            MyType: {
+              type: 'object',
+              properties: {
+                field: { const: 42 },
+              },
+            },
+          },
+        },
+      },
+    ]
+    const result = anthropicToolsToOpenAI(tools as any)
+    const params = result[0].function.parameters as any
+    expect(params.properties.outer.properties.inner).toEqual({ enum: ['fixed'] })
+    expect(params.definitions.MyType.properties.field).toEqual({ enum: [42] })
+  })
+
+  test('sanitizes const in anyOf/oneOf/allOf', () => {
+    const tools = [
+      {
+        type: 'custom',
+        name: 'union',
+        description: 'union test',
+        input_schema: {
+          type: 'object',
+          properties: {
+            val: {
+              anyOf: [
+                { const: 'a' },
+                { const: 'b' },
+                { type: 'string' },
+              ],
+            },
+          },
+        },
+      },
+    ]
+    const result = anthropicToolsToOpenAI(tools as any)
+    const anyOf = (result[0].function.parameters as any).properties.val.anyOf
+    expect(anyOf[0]).toEqual({ enum: ['a'] })
+    expect(anyOf[1]).toEqual({ enum: ['b'] })
+    expect(anyOf[2]).toEqual({ type: 'string' })
+  })
 })
 
 describe('anthropicToolChoiceToOpenAI', () => {

src/services/api/openai/__tests__/streamAdapter.test.ts

@@ -165,6 +165,28 @@ describe('adaptOpenAIStreamToAnthropic', () => {
     expect(msgDelta.delta.stop_reason).toBe('end_turn')
   })
 
+  test('forces tool_use stop_reason when tool_calls present but finish_reason is stop', async () => {
+    // Some backends (e.g., certain OpenAI-compatible endpoints) incorrectly
+    // return finish_reason "stop" when they actually made tool calls.
+    const events = await collectEvents([
+      makeChunk({
+        choices: [{
+          index: 0,
+          delta: {
+            tool_calls: [{ index: 0, id: 'call_1', function: { name: 'bash', arguments: '{"cmd":"ls"}' } }],
+          },
+          finish_reason: null,
+        }],
+      }),
+      makeChunk({
+        choices: [{ index: 0, delta: {}, finish_reason: 'stop' }],
+      }),
+    ])
+
+    const msgDelta = events.find(e => e.type === 'message_delta') as any
+    expect(msgDelta.delta.stop_reason).toBe('tool_use')
+  })
+
   test('maps finish_reason tool_calls to tool_use', async () => {
     const events = await collectEvents([
       makeChunk({

src/services/api/openai/convertTools.ts

@@ -29,12 +29,66 @@ export function anthropicToolsToOpenAI(
         function: {
           name,
           description,
-          parameters: inputSchema || { type: 'object', properties: {} },
+          parameters: sanitizeJsonSchema(inputSchema || { type: 'object', properties: {} }),
         },
       } satisfies ChatCompletionTool
     })
 }
 
+/**
+ * Recursively sanitize a JSON Schema for OpenAI-compatible providers.
+ *
+ * Many OpenAI-compatible endpoints (Ollama, DeepSeek, vLLM, etc.) do not
+ * support the `const` keyword in JSON Schema. Convert it to `enum` with a
+ * single-element array, which is semantically equivalent.
+ */
+function sanitizeJsonSchema(schema: Record<string, unknown>): Record<string, unknown> {
+  if (!schema || typeof schema !== 'object') return schema
+
+  const result = { ...schema }
+
+  // Convert `const` → `enum: [value]`
+  if ('const' in result) {
+    result.enum = [result.const]
+    delete result.const
+  }
+
+  // Recursively process nested schemas
+  const objectKeys = ['properties', 'definitions', '$defs', 'patternProperties'] as const
+  for (const key of objectKeys) {
+    const nested = result[key]
+    if (nested && typeof nested === 'object') {
+      const sanitized: Record<string, unknown> = {}
+      for (const [k, v] of Object.entries(nested as Record<string, unknown>)) {
+        sanitized[k] = v && typeof v === 'object' ? sanitizeJsonSchema(v as Record<string, unknown>) : v
+      }
+      result[key] = sanitized
+    }
+  }
+
+  // Recursively process single-schema keys
+  const singleKeys = ['items', 'additionalProperties', 'not', 'if', 'then', 'else', 'contains', 'propertyNames'] as const
+  for (const key of singleKeys) {
+    const nested = result[key]
+    if (nested && typeof nested === 'object' && !Array.isArray(nested)) {
+      result[key] = sanitizeJsonSchema(nested as Record<string, unknown>)
+    }
+  }
+
+  // Recursively process array-of-schemas keys
+  const arrayKeys = ['anyOf', 'oneOf', 'allOf'] as const
+  for (const key of arrayKeys) {
+    const nested = result[key]
+    if (Array.isArray(nested)) {
+      result[key] = nested.map(item =>
+        item && typeof item === 'object' ? sanitizeJsonSchema(item as Record<string, unknown>) : item
+      )
+    }
+  }
+
+  return result
+}
+
 /**
  * Map Anthropic tool_choice to OpenAI tool_choice format.
  *

src/services/api/openai/streamAdapter.ts

@@ -257,8 +257,12 @@ export async function* adaptOpenAIStreamToAnthropic(
         }
       }
 
-      // Map finish_reason to Anthropic stop_reason
-      const stopReason = mapFinishReason(choice.finish_reason)
+      // Map finish_reason to Anthropic stop_reason.
+      // Some backends return "stop" even when tool_calls are present —
+      // force "tool_use" when we saw any tool blocks to ensure the query
+      // loop actually executes the tools.
+      const hasToolCalls = toolBlocks.size > 0
+      const stopReason = hasToolCalls ? 'tool_use' : mapFinishReason(choice.finish_reason)
 
       yield {
         type: 'message_delta',