refactor(core): upgrade ai-sdk v4 → v6 + Anthropic/openai-compatible reasoning round-trip + max-thinking budget audit

Migrates the LLM stack from [email protected] + @ai-sdk/[email protected] +
@ai-sdk/[email protected] to [email protected] + @ai-sdk/[email protected]
+ @ai-sdk/[email protected]. Full design in plan-v6-upgrade.md;
two rounds of Gemini code review captured in report.md.

Motivation: the recurring 'reasoning-signature without reasoning' error
on Claude Opus 4.7 was a v4 SDK artefact — @ai-sdk/[email protected] emitted
Anthropic signature_delta as a separate stream chunk that orphaned when
the model produced a signed-but-empty thinking block, and our chunk
store had no signature field so the round-trip back to Anthropic was
rejected on the next turn. In v6, signatures arrive inside
providerMetadata on the reasoning-end event, and the orphan-signature
class of bug is gone at the SDK level.

Core changes:
  • ThinkingChunk gains optional metadata?: Record<string, unknown>
    (the v6 providerMetadata blob). A non-undefined metadata 'seals'
    the chunk: subsequent reasoning-delta opens a new chunk rather
    than extending the sealed one.
  • AgentEvent gains { type: 'reasoning-end'; metadata? } (replaces
    the v4 reasoning-signature variant).
  • toModelMessages (replaces toCoreMessages):
      - returns ModelMessage[] (was CoreMessage[])
      - thinking → { type: 'reasoning', text, providerOptions: metadata }
      - tool-batch entries → { type: 'tool-call', input } (was 'args')
      - tool results → { output: { type: 'text', value } } ToolResultOutput
  • Claude OAuth uses createAnthropic({ authToken }) natively — no more
    custom-fetch x-api-key → Bearer swap.
  • rewriteBodyForOpus47 deleted — Opus 4.7 adaptive thinking is native
    via providerOptions.anthropic.thinking = { type: 'adaptive' }.
  • V1 middleware → V3 (specificationVersion: 'v3').
  • v4-era normalizeMessages openai-compatible middleware deleted; the
    v6 openai-compatible provider extracts reasoning_content natively
    from { type: 'reasoning' } content parts.
  • applyAnthropicStructuralNormalisations (mirrors opencode
    provider/transform.ts:53-148): drops empty text/reasoning parts,
    scrubs non-[a-zA-Z0-9_-] toolCallIds, splits [tool-call, non-tool]
    assistant turns (Anthropic rejects tool_use followed by text).
  • applyOpenAICompatibleReasoningNormalisation (mirrors opencode
    transform.ts:217-249): lifts reasoning text into
    providerOptions.openaiCompatible.reasoning_content (always, even
    empty). Solves DeepSeek 'The reasoning_content in the thinking
    mode must be passed back' — the v6 SDK skips emitting
    reasoning_content when text is empty (dist/index.mjs:245), but
    DeepSeek requires the field present once thinking was used.
  • Tools: tool({ inputSchema: jsonSchema(zodToJsonSchema(...)) })
    (was parameters: ZodSchema). AI SDK tools have no execute
    callback — the agent runs tools manually for permission prompts
    and shell-output streaming. New dep: zod-to-json-schema@^3.25.2.
  • fullStream event loop rewritten for v6 event shape: text-delta
    (text not textDelta), reasoning-start/delta/end, tool-input-*,
    tool-call (input not args), tool-result, tool-error (new), abort
    (new), start-step/finish-step, finish.

Max-thinking audit (matches opencode transform.ts:642-671 budgets):
  • Claude enabled-thinking max budget 16000 → 31999 (Anthropic ceiling)
  • Claude enabled-thinking high budget 10000 → 16000
  • maxOutputTokens 'budget + 8000' → fixed 32000 (matches opencode's
    OUTPUT_TOKEN_MAX; model self-allocates thinking vs response within)
  • Opus 4.7 adaptive thinking gains display: 'summarized' and sibling
    effort field (without these, thinking content is hidden by Anthropic
    and the model barely thinks).

Frontend mirrors:
  • types.ts — ThinkingChunk.metadata?, AgentEvent reasoning-end
  • tabs.svelte.ts — routes reasoning-end through applyChunkEvent
  • ChatMessage.svelte — hides empty thinking chunks; hides the entire
    assistant bubble when no chunk has renderable content

Gemini-review-driven fixes:
  • tool-error and abort stream events now surface as error chunks
    (were silently ignored)
  • toolCallId scrubbing pass (opencode transform.ts:96-122 parity)
  • Empty-reasoning-cull explicit test coverage for both Anthropic
    structural normalisation and DeepSeek path

Test counts (223 tests across 3 packages, all green):
  • tests/chunks/append.test.ts: 44 (was 38) — reasoning-end sealing,
    orphan walk-back, multi-block interleaving
  • tests/agent/agent.test.ts: 24 (was 5) — exhaustive v6 event
    mappings, structural normalisations, signature/reasoning_content
    round-trip, tool-error/abort branches, DeepSeek scenario, empty
    reasoning edge case
  • tests/llm/provider.test.ts: 9 (was 22) — dropped 13 obsolete v4
    middleware tests; new minimal tests confirm no middleware wrapping
    on default openai-compat path and that createAnthropic gets
    authToken vs apiKey correctly for OAuth vs api-key flows
  • tests/tools/registry.test.ts: 10 (was 4) — v6 tool() contract
    (inputSchema, no execute, JSON Schema for nested zod)
  • packages/api/tests/agent-manager.test.ts: 12 (was 7) — mock Agent
    emits v6 reasoning events; reasoning-end broadcast + ordering
  • packages/frontend/tests/chat-store.test.ts: 35 (was 32) —
    reasoning-end flow through Svelte $state store

typecheck clean (tsc --noEmit on core + api, svelte-check on frontend),
biome clean across 124 files.

1 files changed, 34 insertions, 14 deletions

diff --git a/packages/core/src/tools/registry.ts b/packages/core/src/tools/registry.ts
index 0c7b110..a09535e 100644
--- a/packages/core/src/tools/registry.ts
+++ b/packages/core/src/tools/registry.ts
@@ -1,7 +1,25 @@
-import { tool } from "ai";
-import { z } from "zod";
+import type { Tool } from "ai";
+import { jsonSchema, tool } from "ai";
+import { zodToJsonSchema } from "zod-to-json-schema";
 import type { ToolDefinition } from "../types/index.js";
 
+/**
+ * Convert an internal `ToolDefinition` (Zod-parameterised) to an AI SDK v6
+ * `Tool` object.
+ *
+ * Critically, NO `execute` function is attached.  The agent's manual tool
+ * loop (see agent.ts) handles execution itself — for permission prompts,
+ * shell-output streaming, and queued-message injection.  Without `execute`,
+ * the SDK never auto-runs tools; it only surfaces `tool-call` events from
+ * `fullStream` that agent.ts collects and dispatches.
+ */
+function toAISDKTool(def: ToolDefinition): Tool {
+	return tool({
+		description: def.description,
+		inputSchema: jsonSchema(zodToJsonSchema(def.parameters)),
+	});
+}
+
 export function createToolRegistry(tools: ToolDefinition[]) {
 	const toolMap = new Map<string, ToolDefinition>(tools.map((t) => [t.name, t]));
 
@@ -14,19 +32,21 @@ export function createToolRegistry(tools: ToolDefinition[]) {
 			return toolMap.get(name);
 		},
 
-		getAISDKTools() {
-			const result: Record<string, ReturnType<typeof tool>> = {};
+		/**
+		 * Returns AI SDK v6 `Tool` objects keyed by tool name, for passing
+		 * directly to `streamText({ tools })`.
+		 *
+		 * Each tool has:
+		 *  - `description`  — forwarded verbatim from the internal definition.
+		 *  - `inputSchema`  — Zod schema converted to JSONSchema7 via
+		 *                     `zod-to-json-schema`, then wrapped with the v6
+		 *                     `jsonSchema()` helper.
+		 *  - NO `execute`   — intentional; see `toAISDKTool` above.
+		 */
+		getAISDKTools(): Record<string, Tool> {
+			const result: Record<string, Tool> = {};
 			for (const [name, def] of toolMap) {
-				const schema = def.parameters;
-				// Do NOT pass execute here — agent.ts handles tool execution
-				// manually via executeToolWithStreaming. Passing execute would
-				// cause the AI SDK to auto-execute tools AND agent.ts to execute
-				// them again, resulting in double execution.
-				const t = tool({
-					description: def.description,
-					parameters: schema instanceof z.ZodObject ? schema : z.object({}),
-				});
-				result[name] = t as unknown as ReturnType<typeof tool>;
+				result[name] = toAISDKTool(def);
 			}
 			return result;
 		},