diff --git a/packages/ai/src/protocols/anthropic-messages.ts b/packages/ai/src/protocols/anthropic-messages.ts
index 1a6bb5af33b4..ef1f19b70313 100644
--- a/packages/ai/src/protocols/anthropic-messages.ts
+++ b/packages/ai/src/protocols/anthropic-messages.ts
@@ -843,6 +843,7 @@ const requireThinkingSignature = (request: LLMRequest) => {
   )
     return false
   if (provider.includes("xiaomi") || model.includes("mimo") || baseURL.includes("xiaomimimo.com")) return false
+  if (model.startsWith("qwen") || model.startsWith("minimax-")) return false
   return true
 }
 
@@ -971,19 +972,9 @@ const lowerMessages = Effect.fnUntraced(function* (request: LLMRequest, breakpoi
             continue
           }
           if (!signature || signature.trim().length === 0) {
-            if (part.text.trim().length === 0) continue
-            if (!requireThinkingSignature(request)) {
+            if (part.text.trim().length > 0 && !requireThinkingSignature(request)) {
               content.push({ type: "thinking", thinking: part.text, signature: "" })
-              continue
             }
-            // Without a signature this cannot be a valid thinking block per
-            // the SDK ThinkingBlockParam:3217 — demote to text so the
-            // conversation remains sendable.
-            content.push({
-              type: "text",
-              text: part.text,
-              cache_control: cacheControl(breakpoints, part.cache),
-            })
             continue
           }
           content.push({ type: "thinking", thinking: part.text, signature })
diff --git a/packages/ai/src/protocols/bedrock-converse.ts b/packages/ai/src/protocols/bedrock-converse.ts
index e86a77334ae3..353f2b09d6e4 100644
--- a/packages/ai/src/protocols/bedrock-converse.ts
+++ b/packages/ai/src/protocols/bedrock-converse.ts
@@ -427,12 +427,7 @@ const lowerMessages = Effect.fnUntraced(function* (
             content.push({ reasoningContent: { redactedContent: redactedData } })
             continue
           }
-          if (signature === undefined || signature.trim().length === 0) {
-            // Interrupted streams and model switches can leave unsigned reasoning.
-            // Preserve readable history as text rather than replay invalid reasoningContent.
-            if (part.text.trim().length > 0) content.push(...textWithCache(breakpoints, part.text, part.cache))
-            continue
-          }
+          if (signature === undefined || signature.trim().length === 0) continue
           content.push({ reasoningContent: { reasoningText: { text: part.text, signature } } })
           continue
         }
diff --git a/packages/ai/src/protocols/gemini.ts b/packages/ai/src/protocols/gemini.ts
index 29218420003f..be9e929ca208 100644
--- a/packages/ai/src/protocols/gemini.ts
+++ b/packages/ai/src/protocols/gemini.ts
@@ -32,22 +32,12 @@ import { Lifecycle } from "./utils/lifecycle.js"
 
 const ADAPTER = "gemini"
 const CONTINUATION = "CONTINUATION"
-// Google documents this sentinel for replaying Gemini 3 function calls after their original signature was lost.
+// Google documents this sentinel for replaying function calls after their original signature was lost.
 const SKIP_THOUGHT_SIGNATURE_VALIDATOR = "skip_thought_signature_validator"
 // Gemini 2.5 rejects a budget under the model's minimum: 512 on Flash-Lite, the highest, and 128 on Pro.
 const MIN_THINKING_BUDGET = 512
 export const DEFAULT_BASE_URL = "https://generativelanguage.googleapis.com/v1beta"
 
-// Gemini 3 rejects replayed function calls without a thought signature. Google's SDKs avoid that in normal chats by
-// retaining complete model responses, but OpenCode reconstructs durable history and may encounter an unsigned call
-// from an older or external session. Model IDs are open-ended, so unknown Gemini aliases inherit current behavior.
-const requiresThoughtSignatureFallback = (modelID: string) => {
-  if (!/(^|\/)gemini-/i.test(modelID)) return false
-  if (/(^|\/)gemini-(?:1|2)(?:[.-]|$)/i.test(modelID)) return false
-  if (/(^|\/)gemini-pro(?:-vision)?$/i.test(modelID)) return false
-  return !/(^|\/)gemini-robotics-er-1\.5(?:[.-]|$)/i.test(modelID)
-}
-
 // Gemini 3 accepts media nested inside function responses; matched Gemini 2.5 variants reject it,
 // so their tool-result attachments lower as a separate user turn instead.
 const routesLegacyToolMedia = (modelID: string) => /gemini-2[.-]5(?:[.-]|$)/i.test(modelID)
@@ -390,11 +380,7 @@ const lowerMessages = Effect.fnUntraced(function* (request: LLMRequest) {
           const signature = lowered.thoughtSignature
           parts.push({
             ...lowered,
-            thoughtSignature:
-              signature ??
-              (requiresThoughtSignatureFallback(request.model.id) && !hasSignedToolCall
-                ? SKIP_THOUGHT_SIGNATURE_VALIDATOR
-                : undefined),
+            thoughtSignature: signature ?? (!hasSignedToolCall ? SKIP_THOUGHT_SIGNATURE_VALIDATOR : undefined),
           })
           if (signature !== undefined) hasSignedToolCall = true
           continue
diff --git a/packages/ai/src/protocols/google-interactions.ts b/packages/ai/src/protocols/google-interactions.ts
index a04083fd0783..24d2179afb19 100644
--- a/packages/ai/src/protocols/google-interactions.ts
+++ b/packages/ai/src/protocols/google-interactions.ts
@@ -23,6 +23,7 @@ import { GeminiGenerateContent } from "./utils/gemini-generate-content.js"
 import { ToolStream } from "./utils/tool-stream.js"
 
 const ADAPTER = "google-interactions"
+const SKIP_THOUGHT_SIGNATURE_VALIDATOR = "skip_thought_signature_validator"
 export const DEFAULT_BASE_URL = "https://generativelanguage.googleapis.com/v1beta"
 
 // =============================================================================
@@ -259,6 +260,7 @@ const lowerMessages = Effect.fnUntraced(function* (request: LLMRequest) {
         steps[steps.length - 1] = { type, content: [...last.content, content] }
       else steps.push({ type, content: [content] })
     }
+    let hasSignedStep = false
     for (const part of message.content) {
       if (message.role === "tool") {
         if (part.type !== "tool-result")
@@ -281,21 +283,25 @@ const lowerMessages = Effect.fnUntraced(function* (request: LLMRequest) {
         continue
       }
       if (message.role === "assistant" && part.type === "reasoning") {
+        const thoughtSignature = signature(part.providerMetadata, key)
         steps.push({
           type: "thought",
-          signature: signature(part.providerMetadata, key),
+          signature: thoughtSignature,
           summary: part.text ? [{ type: "text", text: part.text }] : undefined,
         })
+        if (thoughtSignature !== undefined) hasSignedStep = true
         continue
       }
       if (message.role === "assistant" && part.type === "tool-call") {
+        const toolSignature = signature(part.providerMetadata, key)
         steps.push({
           type: "function_call",
           id: part.id,
           name: part.name,
           arguments: part.input,
-          signature: signature(part.providerMetadata, key),
+          signature: toolSignature ?? (!hasSignedStep ? SKIP_THOUGHT_SIGNATURE_VALIDATOR : undefined),
         })
+        if (toolSignature !== undefined) hasSignedStep = true
         continue
       }
       return yield* ProviderShared.unsupportedContent(
diff --git a/packages/ai/src/protocols/mistral-chat.ts b/packages/ai/src/protocols/mistral-chat.ts
index 619f169d2a2a..4c1fbfbab8f1 100644
--- a/packages/ai/src/protocols/mistral-chat.ts
+++ b/packages/ai/src/protocols/mistral-chat.ts
@@ -254,7 +254,6 @@ const lowerToolCall = (part: ToolCallPart, normalizeID: (id: string) => string):
 const lowerAssistant = Effect.fnUntraced(function* (
   message: LLMRequest["messages"][number],
   normalizeID: (id: string) => string,
-  prefix: boolean,
 ) {
   const structured = message.content.some(
     (part) => part.type === "reasoning" && isMistralThinkingContent(part.providerMetadata?.mistral?.thinking),
@@ -271,8 +270,6 @@ const lowerAssistant = Effect.fnUntraced(function* (
     if (part.type === "reasoning") {
       const native = part.providerMetadata?.mistral?.thinking
       if (structured && isMistralThinkingContent(native)) content.push(native)
-      else if (structured) content.push({ type: "text", text: part.text })
-      else text.push(part.text)
       continue
     }
     if (part.type === "tool-call") {
@@ -285,7 +282,6 @@ const lowerAssistant = Effect.fnUntraced(function* (
     role: "assistant" as const,
     content: structured ? content : text.join(""),
     ...(toolCalls.length > 0 ? { tool_calls: toolCalls } : {}),
-    ...(prefix ? { prefix: true as const } : {}),
   }
 })
 
@@ -358,15 +354,17 @@ const lowerMessages = Effect.fnUntraced(function* (request: LLMRequest) {
       const hasNativeThinking = message.content.some(
         (part) => part.type === "reasoning" && isMistralThinkingContent(part.providerMetadata?.mistral?.thinking),
       )
-      const text = message.content
-        .flatMap((part) => (part.type === "text" || part.type === "reasoning" ? [part.text] : []))
-        .join("")
+      const text = message.content.flatMap((part) => (part.type === "text" ? [part.text] : [])).join("")
       if (!hasToolCalls && !hasNativeThinking && text.trim() === "") continue
-      messages.push(yield* lowerAssistant(message, normalizeID, !hasToolCalls && message === request.messages.at(-1)))
+      messages.push(yield* lowerAssistant(message, normalizeID))
       continue
     }
     messages.push(...(yield* lowerToolResults(message, normalizeID)))
   }
+  const trailing = messages.at(-1)
+  if (trailing?.role === "assistant" && !trailing.tool_calls) {
+    messages[messages.length - 1] = { ...trailing, prefix: true }
+  }
   return messages
 })
 
diff --git a/packages/ai/src/providers/meta.ts b/packages/ai/src/providers/meta.ts
index eecbb8125479..13fac64f3b4f 100644
--- a/packages/ai/src/providers/meta.ts
+++ b/packages/ai/src/providers/meta.ts
@@ -138,7 +138,6 @@ export const configure = (input: Config = {}) => {
   const messages = (modelID: string | ModelID) =>
     configuredMessages.model<MessagesOptionsInput>({
       id: modelID,
-      compatibility: { requireSignature: false },
     })
   const media = MediaRoute.deployment(input, options.auth)
   const image = (modelID: string | ModelID) => MetaImages.model({ ...media, id: modelID })
diff --git a/packages/ai/src/providers/minimax.ts b/packages/ai/src/providers/minimax.ts
index 18c69016199c..ec5d77e7333b 100644
--- a/packages/ai/src/providers/minimax.ts
+++ b/packages/ai/src/providers/minimax.ts
@@ -117,7 +117,10 @@ export const configure = (input: Config = {}) => {
     auth,
   }
   const messages = (modelID: string | ModelID) =>
-    messagesRoute.with(defaults).model<MessagesOptionsInput>({ id: modelID })
+    messagesRoute.with(defaults).model<MessagesOptionsInput>({
+      id: modelID,
+      compatibility: { requireSignature: false },
+    })
   const chat = (modelID: string | ModelID) =>
     chatRoute.with(defaults).model<ChatOptionsInput>({
       id: modelID,
diff --git a/packages/ai/test/provider/anthropic-messages.test.ts b/packages/ai/test/provider/anthropic-messages.test.ts
index 41dcc6decb5f..0ba341755951 100644
--- a/packages/ai/test/provider/anthropic-messages.test.ts
+++ b/packages/ai/test/provider/anthropic-messages.test.ts
@@ -1035,13 +1035,11 @@ describe("Anthropic Messages route", () => {
     }),
   )
 
-  it.effect("demotes unsigned reasoning when signatures are required", () =>
+  it.effect("drops unsigned reasoning when signatures are required", () =>
     Effect.gen(function* () {
       const prepared = yield* compileUnsignedReasoning(model)
 
-      expect(prepared.body.messages).toEqual([
-        { role: "assistant", content: [{ type: "text", text: "unsigned reasoning" }] },
-      ])
+      expect(prepared.body.messages).toEqual([])
     }),
   )
 
@@ -1061,19 +1059,19 @@ describe("Anthropic Messages route", () => {
         .model({ id: "kimi-k2.6" })
       const codingPrepared = yield* compileUnsignedReasoning(coding.model({ id: "k3" }))
       const moonshotPrepared = yield* compileUnsignedReasoning(moonshot)
+      const qwenPrepared = yield* compileUnsignedReasoning(coding.with({ provider: "opencode" }).model({ id: "qwen3.8-flash" }))
+      const minimaxPrepared = yield* compileUnsignedReasoning(
+        coding.with({ provider: "opencode-go" }).model({ id: "minimax-m3" }),
+      )
 
-      expect(codingPrepared.body.messages).toEqual([
-        {
-          role: "assistant",
-          content: [{ type: "thinking", thinking: "unsigned reasoning", signature: "" }],
-        },
-      ])
-      expect(moonshotPrepared.body.messages).toEqual([
-        {
-          role: "assistant",
-          content: [{ type: "thinking", thinking: "unsigned reasoning", signature: "" }],
-        },
-      ])
+      for (const prepared of [codingPrepared, moonshotPrepared, qwenPrepared, minimaxPrepared]) {
+        expect(prepared.body.messages).toEqual([
+          {
+            role: "assistant",
+            content: [{ type: "thinking", thinking: "unsigned reasoning", signature: "" }],
+          },
+        ])
+      }
     }),
   )
 
@@ -1088,9 +1086,7 @@ describe("Anthropic Messages route", () => {
         .model({ id: "k3", compatibility: { requireSignature: true } })
       const prepared = yield* compileUnsignedReasoning(compatible)
 
-      expect(prepared.body.messages).toEqual([
-        { role: "assistant", content: [{ type: "text", text: "unsigned reasoning" }] },
-      ])
+      expect(prepared.body.messages).toEqual([])
     }),
   )
 
diff --git a/packages/ai/test/provider/bedrock-converse-cache.test.ts b/packages/ai/test/provider/bedrock-converse-cache.test.ts
index 3ec178fdcec5..263ebd3b7772 100644
--- a/packages/ai/test/provider/bedrock-converse-cache.test.ts
+++ b/packages/ai/test/provider/bedrock-converse-cache.test.ts
@@ -61,7 +61,7 @@ describe("Bedrock Converse cache policy", () => {
               { role: "user", content: [{ text: "Question" }, { text: "<system-update>\nUpdate\n</system-update>" }] },
               {
                 role: "assistant",
-                content: [{ text: "Answer" }, { text: "Unsigned reasoning" }, { toolUse: { name: "lookup" } }],
+                content: [{ text: "Answer" }, { toolUse: { name: "lookup" } }],
               },
               { role: "user", content: [{ toolResult: { content: [{ json: "Result" }] } }] },
             ],
diff --git a/packages/ai/test/provider/bedrock-converse.test.ts b/packages/ai/test/provider/bedrock-converse.test.ts
index 99e0e72e17b0..8464b9137930 100644
--- a/packages/ai/test/provider/bedrock-converse.test.ts
+++ b/packages/ai/test/provider/bedrock-converse.test.ts
@@ -1197,7 +1197,7 @@ describe("Bedrock Converse route", () => {
 
   for (const signature of [undefined, "", "   "]) {
     for (const cache of ["none", "auto"] as const) {
-      it.effect(`demotes unsigned reasoning to text (${JSON.stringify(signature)}, cache: ${cache})`, () =>
+      it.effect(`drops unsigned reasoning (${JSON.stringify(signature)}, cache: ${cache})`, () =>
         Effect.gen(function* () {
           const prepared = yield* compileRequest(
             ai.request({
@@ -1217,10 +1217,15 @@ describe("Bedrock Converse route", () => {
               cache,
             }),
           )
-          expect(prepared.body.messages[1]).toEqual({
-            role: "assistant",
-            content: [{ text: "Partial thought" }, { cachePoint: { type: "default" } }],
-          })
+          expect(prepared.body.messages).toEqual([
+            {
+              role: "user",
+              content:
+                cache === "auto"
+                  ? [{ text: "Think" }, { text: "Continue" }, { cachePoint: { type: "default" } }]
+                  : [{ text: "Think" }, { text: "Continue" }],
+            },
+          ])
         }),
       )
     }
@@ -1252,7 +1257,7 @@ describe("Bedrock Converse route", () => {
     }),
   )
 
-  it.effect("demotes foreign reasoning while preserving signed, redacted, text, and tool blocks", () =>
+  it.effect("drops foreign reasoning while preserving signed, redacted, text, and tool blocks", () =>
     Effect.gen(function* () {
       const cache = new CacheHint({ type: "ephemeral" })
       const prepared = yield* compileRequest(
@@ -1281,7 +1286,6 @@ describe("Bedrock Converse route", () => {
         {
           role: "assistant",
           content: [
-            { text: "Foreign thought" },
             { reasoningContent: { reasoningText: { text: "Signed thought", signature: "sig_1" } } },
             { reasoningContent: { reasoningText: { text: "", signature: "sig_2" } } },
             { reasoningContent: { redactedContent: "cmVkYWN0ZWQ=" } },
diff --git a/packages/ai/test/provider/gemini.test.ts b/packages/ai/test/provider/gemini.test.ts
index 22bda497745f..7a0bd6e57afc 100644
--- a/packages/ai/test/provider/gemini.test.ts
+++ b/packages/ai/test/provider/gemini.test.ts
@@ -175,7 +175,12 @@ describe("Gemini route", () => {
       expect(prepared.body.contents).toEqual([
         {
           role: "model",
-          parts: [{ functionCall: { name: "lookup", args: { query: "weather" } } }],
+          parts: [
+            {
+              functionCall: { name: "lookup", args: { query: "weather" } },
+              thoughtSignature: "skip_thought_signature_validator",
+            },
+          ],
         },
         {
           role: "user",
@@ -219,8 +224,14 @@ describe("Gemini route", () => {
         {
           role: "model",
           parts: [
-            { functionCall: { name: "lookup", args: { query: "weather" } } },
-            { functionCall: { name: "lookup", args: { query: "time" } } },
+            {
+              functionCall: { name: "lookup", args: { query: "weather" } },
+              thoughtSignature: "skip_thought_signature_validator",
+            },
+            {
+              functionCall: { name: "lookup", args: { query: "time" } },
+              thoughtSignature: "skip_thought_signature_validator",
+            },
           ],
         },
         {
@@ -302,7 +313,15 @@ describe("Gemini route", () => {
       )
 
       expect(legacy.body.contents).toEqual([
-        { role: "model", parts: [{ functionCall: { name: "lookup", args: { query: "weather" } } }] },
+        {
+          role: "model",
+          parts: [
+            {
+              functionCall: { name: "lookup", args: { query: "weather" } },
+              thoughtSignature: "skip_thought_signature_validator",
+            },
+          ],
+        },
         {
           role: "user",
           parts: [{ functionResponse: { name: "lookup", response: { name: "lookup", content: "done" } } }],
@@ -331,7 +350,15 @@ describe("Gemini route", () => {
       )
 
       expect(prepared.body.contents).toEqual([
-        { role: "model", parts: [{ functionCall: { id: "call_1", name: "lookup", args: { query: "weather" } } }] },
+        {
+          role: "model",
+          parts: [
+            {
+              functionCall: { id: "call_1", name: "lookup", args: { query: "weather" } },
+              thoughtSignature: "skip_thought_signature_validator",
+            },
+          ],
+        },
         {
           role: "user",
           parts: [
@@ -380,7 +407,12 @@ describe("Gemini route", () => {
           },
           {
             role: "model",
-            parts: [{ functionCall: { name: "lookup", args: { query: "weather" } } }],
+            parts: [
+              {
+                functionCall: { name: "lookup", args: { query: "weather" } },
+                thoughtSignature: "skip_thought_signature_validator",
+              },
+            ],
           },
           {
             role: "user",
@@ -434,7 +466,15 @@ describe("Gemini route", () => {
       )
 
       expect(prepared.body.contents).toEqual([
-        { role: "model", parts: [{ functionCall: { name: "read", args: { path: "pixel.png" } } }] },
+        {
+          role: "model",
+          parts: [
+            {
+              functionCall: { name: "read", args: { path: "pixel.png" } },
+              thoughtSignature: "skip_thought_signature_validator",
+            },
+          ],
+        },
         {
           role: "user",
           parts: [
@@ -608,7 +648,13 @@ describe("Gemini route", () => {
         model: "gemini-3-flash-preview",
         input: [
           { type: "user_input", content: [{ type: "video", uri, mime_type: "video/mp4" }] },
-          { type: "function_call", id: "call_video", name: "read", arguments: {} },
+          {
+            type: "function_call",
+            id: "call_video",
+            name: "read",
+            arguments: {},
+            signature: "skip_thought_signature_validator",
+          },
           {
             type: "function_result",
             call_id: "call_video",
@@ -652,7 +698,10 @@ describe("Gemini route", () => {
       )
 
       expect(prepared.body.contents).toEqual([
-        { role: "model", parts: [{ functionCall: { name: "shot", args: {} } }] },
+        {
+          role: "model",
+          parts: [{ functionCall: { name: "shot", args: {} }, thoughtSignature: "skip_thought_signature_validator" }],
+        },
         {
           role: "user",
           parts: [{ functionResponse: { name: "shot", response: { name: "shot", content: "" } } }],
@@ -702,7 +751,10 @@ describe("Gemini route", () => {
       expect(prepared.body.contents).toEqual([
         {
           role: "model",
-          parts: [{ functionCall: { name: "shot", args: {} } }, { functionCall: { name: "shot", args: {} } }],
+          parts: [
+            { functionCall: { name: "shot", args: {} }, thoughtSignature: "skip_thought_signature_validator" },
+            { functionCall: { name: "shot", args: {} }, thoughtSignature: "skip_thought_signature_validator" },
+          ],
         },
         {
           role: "user",
diff --git a/packages/ai/test/provider/google-vertex-interactions.test.ts b/packages/ai/test/provider/google-vertex-interactions.test.ts
index e3b34d021696..172e0ddd1dcc 100644
--- a/packages/ai/test/provider/google-vertex-interactions.test.ts
+++ b/packages/ai/test/provider/google-vertex-interactions.test.ts
@@ -259,6 +259,49 @@ describe("Google Vertex Interactions", () => {
         ],
       })
       expect(prepared.body.previous_interaction_id).toBeUndefined()
+
+      const unsigned = yield* compileRequest(
+        ai.request({
+          model,
+          messages: [
+            Message.assistant([
+              ToolCallPart.make({ id: "call_foreign", name: "lookup", input: { city: "Paris" } }),
+            ]),
+            Message.tool({ id: "call_foreign", name: "lookup", result: { weather: "sunny" } }),
+            Message.assistant([
+              ToolCallPart.make({
+                id: "call_signed",
+                name: "lookup",
+                input: { city: "Lyon" },
+                providerMetadata: { vertex: { interactionSignature: "sig_1" } },
+              }),
+              ToolCallPart.make({ id: "call_sibling", name: "lookup", input: { city: "Nice" } }),
+            ]),
+            Message.tool({ id: "call_signed", name: "lookup", result: { weather: "cloudy" } }),
+            Message.tool({ id: "call_sibling", name: "lookup", result: { weather: "warm" } }),
+          ],
+        }),
+      )
+      expect(unsigned.body.input).toEqual([
+        {
+          type: "function_call",
+          id: "call_foreign",
+          name: "lookup",
+          arguments: { city: "Paris" },
+          signature: "skip_thought_signature_validator",
+        },
+        { type: "function_result", call_id: "call_foreign", name: "lookup", result: { weather: "sunny" } },
+        {
+          type: "function_call",
+          id: "call_signed",
+          name: "lookup",
+          arguments: { city: "Lyon" },
+          signature: "sig_1",
+        },
+        { type: "function_call", id: "call_sibling", name: "lookup", arguments: { city: "Nice" } },
+        { type: "function_result", call_id: "call_signed", name: "lookup", result: { weather: "cloudy" } },
+        { type: "function_result", call_id: "call_sibling", name: "lookup", result: { weather: "warm" } },
+      ])
     }),
   )
 })
diff --git a/packages/ai/test/provider/mistral-chat.test.ts b/packages/ai/test/provider/mistral-chat.test.ts
index ded7bf59e5ec..6efdedf04bae 100644
--- a/packages/ai/test/provider/mistral-chat.test.ts
+++ b/packages/ai/test/provider/mistral-chat.test.ts
@@ -123,7 +123,7 @@ describe("Mistral Chat", () => {
         },
         {
           role: "assistant",
-          content: "ThinkCalling",
+          content: "Calling",
         },
       ])
       const assistant = prepared.body.messages[3]
@@ -177,6 +177,21 @@ describe("Mistral Chat", () => {
         { role: "assistant", content: "Prefix", prefix: true },
       ])
 
+      const trailingDropped = yield* compileRequest(
+        ai.request({
+          model,
+          messages: [
+            Message.user("Continue"),
+            Message.assistant("Prefix"),
+            Message.assistant({ type: "reasoning", text: "Dropped unsigned reasoning" }),
+          ],
+        }),
+      )
+      expect(trailingDropped.body.messages).toEqual([
+        { role: "user", content: "Continue" },
+        { role: "assistant", content: "Prefix", prefix: true },
+      ])
+
       const uncached = yield* compileRequest(
         ai.request({
           model,
@@ -227,6 +242,7 @@ describe("Mistral Chat", () => {
           messages: [
             Message.assistant(" \n "),
             Message.assistant({ type: "reasoning", text: "\t" }),
+            Message.assistant({ type: "reasoning", text: "Foreign reasoning without mistral metadata" }),
             Message.assistant({ type: "tool-call", id: "Ab12Cd34E", name: "lookup", input: {} }),
           ],
         }),
diff --git a/packages/core/src/session/runner/to-llm-message.ts b/packages/core/src/session/runner/to-llm-message.ts
index 3d8921c0911b..26750bfec515 100644
--- a/packages/core/src/session/runner/to-llm-message.ts
+++ b/packages/core/src/session/runner/to-llm-message.ts
@@ -171,8 +171,9 @@ const assistant = (message: SessionMessage.Assistant, model: Model.Ref, provider
         },
       ]
     // Let the destination adapter handle readable reasoning after a model/provider switch.
-    if (item.type === "reasoning")
-      return reuseProviderMetadata && !reasoningInterrupted
+    if (item.type === "reasoning") {
+      if (message.error !== undefined || reasoningInterrupted) return []
+      return reuseProviderMetadata
         ? [
             {
               type: "reasoning",
@@ -181,8 +182,9 @@ const assistant = (message: SessionMessage.Assistant, model: Model.Ref, provider
             },
           ]
         : item.text.length > 0
-          ? [{ type: message.error === undefined && !reasoningInterrupted ? "reasoning" : "text", text: item.text }]
+          ? [{ type: "reasoning", text: item.text }]
           : []
+    }
     // Call-side metadata is model-scoped proof of generation (Gemini thought
     // signatures, OpenAI encrypted reasoning): only the producing model may
     // replay it.
diff --git a/packages/core/test/session-runner-message.test.ts b/packages/core/test/session-runner-message.test.ts
index ed9265766cc6..c81143d34e9d 100644
--- a/packages/core/test/session-runner-message.test.ts
+++ b/packages/core/test/session-runner-message.test.ts
@@ -933,7 +933,7 @@ Earlier work
     ])
   })
 
-  test("lowers failed assistant reasoning to text", () => {
+  test("drops failed assistant reasoning while preserving settled hosted tools", () => {
     const messages = toLLMMessages(
       [
         SessionMessage.Assistant.make({
@@ -983,7 +983,6 @@ Earlier work
     )
 
     expect(messages[0]?.content).toEqual([
-      { type: "text", text: "Partial thought" },
       {
         type: "tool-call",
         id: "hosted-completed",
@@ -1029,7 +1028,7 @@ Earlier work
     ])
   })
 
-  test("drops unfinished reasoning metadata from an interrupted assistant message", () => {
+  test("omits unfinished reasoning from an interrupted assistant message", () => {
     const messages = toLLMMessages(
       [
         SessionMessage.Assistant.make({
@@ -1057,7 +1056,7 @@ Earlier work
       model,
     )
 
-    expect(messages[0]?.content).toEqual([{ type: "text", text: "Completed summary part" }])
+    expect(messages).toEqual([])
   })
 
   test("drops model-scoped continuation metadata after a model switch but keeps hosted result payloads", () => {
diff --git a/packages/core/test/session-runner.test.ts b/packages/core/test/session-runner.test.ts
index ce2dc61e1b2e..948d3d861768 100644
--- a/packages/core/test/session-runner.test.ts
+++ b/packages/core/test/session-runner.test.ts
@@ -6153,7 +6153,7 @@ describe("SessionRunnerLLM", () => {
     ])
   })
 
-  scenario("lowers interrupted reasoning before continuing an incomplete stream", function* (s) {
+  scenario("drops interrupted reasoning before continuing an incomplete stream", function* (s) {
     yield* s.admit("Continue interrupted reasoning")
     yield* s.llm.push(
       TestLLM.failAfter(
@@ -6171,19 +6171,10 @@ describe("SessionRunnerLLM", () => {
     yield* TestClock.adjust("2400 millis")
     yield* Fiber.join(run)
 
-    expect(s.requests[1]?.messages.at(-2)).toMatchObject({
-      role: "assistant",
-      content: [{ type: "text", text: "Partial thought" }],
-    })
-    expect(s.requests[1]?.messages.at(-1)).toMatchObject({
-      role: "user",
-      content: [
-        {
-          type: "text",
-          text: INCOMPLETE_STREAM_CONTINUATION,
-        },
-      ],
-    })
+    expect(s.requests[1]?.messages.slice(-2)).toMatchObject([
+      { role: "user", content: [{ type: "text", text: "Continue interrupted reasoning" }] },
+      { role: "user", content: [{ type: "text", text: INCOMPLETE_STREAM_CONTINUATION }] },
+    ])
     expect(yield* s.context).toMatchObject([
       { type: "user" },
       Expected.assistant({ finish: "error" }, [Expected.reasoning("Partial thought")]),