fix: address PR review follow-ups — rebase, parity, tests, safety

- Rebase onto main (resolve solid-chat + e2e merge conflicts)
- Extend `const TTools` to Preact `useChat` and Angular `injectChat`
- Add message-updaters tests for `input` carry-forward through approval
- Guard `JSON.stringify(chunk.input)` in stream processor
- Strengthen approval-gating changeset migration notes; include angular/preact
  in the const-tools inference changeset

Author: tombeckenham

.changeset/tool-call-approval-gating.md

@@ -20,12 +20,36 @@ for (const part of message.parts) {
 }
 ```
 
-**Breaking (types only):** when you pass typed `tools`, reading `part.approval`
-on a mixed tool-call union without first narrowing by `part.name` no longer
-compiles — narrow to a `needsApproval: true` tool first. Untyped `useChat()`
-(no `tools` generic) and the base `ToolCallPart` type are unaffected: `approval`
-stays available on every tool-call part there. Runtime behavior is unchanged.
+## ⚠️ Breaking change (types only)
+
+**This is the primary migration surface for this release.** When you pass a typed
+`tools` array to `useChat` / `createChat` / `injectChat`, reading `part.approval`
+on a mixed tool-call union **without first narrowing by `part.name`** no longer
+compiles. Code that previously did `part.approval?.id` in a generic handler over
+all tool-call parts must be updated:
+
+```ts
+// ❌ No longer compiles on a typed mixed union
+part.approval?.id
+
+// ✅ Narrow to an approval-required tool first
+if (part.name === 'deleteAccount') part.approval?.id
+
+// ✅ Or guard with `in`
+if ('approval' in part) part.approval?.id
+
+// ✅ Or type the handler against the base (untyped) ToolCallPart
+function handleApproval(part: ToolCallPart) {
+  return part.approval?.id
+}
+```
+
+Untyped `useChat()` (no inferred `tools` generic) and the base `ToolCallPart`
+type are unaffected: `approval` stays available on every tool-call part there.
+**Runtime behavior is unchanged** — only TypeScript narrowing is stricter.
 
 Adds a `TNeedsApproval extends boolean` type parameter (defaulting to `false`)
 to the client tool types; existing explicit type arguments keep working via the
-default.
+default. Literal capture requires `toolDefinition({ needsApproval: true })` at
+the call site — a dynamic `needsApproval: boolean` variable will not gate the
+type.

.changeset/usechat-const-tools-inference.md

@@ -1,16 +1,18 @@
 ---
+'@tanstack/ai-angular': patch
+'@tanstack/ai-preact': patch
 '@tanstack/ai-react': patch
 '@tanstack/ai-solid': patch
 '@tanstack/ai-svelte': patch
 '@tanstack/ai-vue': patch
 ---
 
 Add the `const` modifier to the `TTools` type parameter of `useChat`
-(`createChat` in Svelte) so a plain inline `tools` array now yields full
-type-safe message chunks. Previously the array widened to
+(`createChat` in Svelte, `injectChat` in Angular) so a plain inline `tools` array
+now yields full type-safe message chunks. Previously the array widened to
 `Array<Union>` and lost the literal tool `name`s that drive the
 discriminated `tool-call` part union, so callers had to wrap their tools in
 `clientTools(...)` (or add `as const`) to get narrowing. That wrapper is now
 optional — `tools: [toolA, toolB]` narrows `part.name`, `part.input`, and
 `part.output` on its own. `clientTools(...)` still works and remains useful
-for defining a shared tuple outside the hook call.
+for defining a shared tuple outside the hook call.

packages/ai-angular/src/inject-chat.ts

@@ -35,7 +35,7 @@ import type {
 let nextId = 0
 
 export function injectChat<
-  TTools extends ReadonlyArray<AnyClientTool> = any,
+  const TTools extends ReadonlyArray<AnyClientTool> = any,
   TSchema extends SchemaInput | undefined = undefined,
   TContext = InferredClientContext<TTools>,
 >(

packages/ai-preact/src/use-chat.ts

@@ -23,7 +23,7 @@ import type {
 } from './types'
 
 export function useChat<
-  TTools extends ReadonlyArray<AnyClientTool> = any,
+  const TTools extends ReadonlyArray<AnyClientTool> = any,
   TContext = InferredClientContext<TTools>,
 >(options: UseChatOptions<TTools, TContext>): UseChatReturn<TTools> {
   const hookId = useId()

packages/ai/src/activities/chat/stream/processor.ts

@@ -1298,7 +1298,12 @@ export class StreamProcessor {
       // received, back-fill the arguments string so the UIMessage ToolCallPart
       // carries the correct value (defensive against adapters that skip ARGS).
       if (chunk.input !== undefined && !existingToolCall.arguments) {
-        existingToolCall.arguments = JSON.stringify(chunk.input)
+        try {
+          existingToolCall.arguments = JSON.stringify(chunk.input)
+        } catch {
+          // circular refs, BigInt, etc. — leave arguments empty rather than
+          // aborting stream processing
+        }
       }
 
       const index = msgState.toolCallOrder.indexOf(chunk.toolCallId)

packages/ai/tests/message-updaters.test.ts

@@ -244,6 +244,59 @@ describe('message-updaters', () => {
       })
     })
 
+    it('should preserve existing input when updating a tool call without input in payload', () => {
+      const parsedInput = { path: '/tmp/file' }
+      const messages = [
+        createMessage('msg-1', 'assistant', [
+          {
+            type: 'tool-call',
+            id: 'call-1',
+            name: 'deleteFile',
+            arguments: '{"path":"/tmp/file"}',
+            state: 'input-complete',
+            input: parsedInput,
+          },
+        ]),
+      ]
+
+      const result = updateToolCallPart(messages, 'msg-1', {
+        id: 'call-1',
+        name: 'deleteFile',
+        arguments: '{"path":"/tmp/file"}',
+        state: 'approval-requested',
+      })
+
+      const part = result[0]?.parts[0] as ToolCallPart | undefined
+      expect(part?.input).toEqual(parsedInput)
+    })
+
+    it('should preserve existing input through approval request updates', () => {
+      const parsedInput = { path: '/tmp/file' }
+      const messages = [
+        createMessage('msg-1', 'assistant', [
+          {
+            type: 'tool-call',
+            id: 'call-1',
+            name: 'deleteFile',
+            arguments: '{"path":"/tmp/file"}',
+            state: 'input-complete',
+            input: parsedInput,
+          },
+        ]),
+      ]
+
+      const result = updateToolCallApproval(
+        messages,
+        'msg-1',
+        'call-1',
+        'approval-123',
+      )
+
+      const part = result[0]?.parts[0] as ToolCallPart | undefined
+      expect(part?.input).toEqual(parsedInput)
+      expect(part?.state).toBe('approval-requested')
+    })
+
     it('should preserve existing output when updating a tool call', () => {
       const toolOutput = { temperature: 20, conditions: 'sunny' }
       const messages = [