diff --git a/src/__tests__/transform-parity.test.ts b/src/__tests__/transform-parity.test.ts
index 3d4f5cc8..3f86e665 100644
--- a/src/__tests__/transform-parity.test.ts
+++ b/src/__tests__/transform-parity.test.ts
@@ -12,6 +12,9 @@ import { droidAdapter } from "../proxy/adapters/droid"
 import { piAdapter } from "../proxy/adapters/pi"
 import { forgeCodeAdapter } from "../proxy/adapters/forgecode"
 import { passthroughAdapter } from "../proxy/adapters/passthrough"
+import { claudeCodeTransforms } from "../proxy/transforms/claudecode"
+import { claudeCodeAdapter } from "../proxy/adapters/claudecode"
+import { getAdapterTransforms } from "../proxy/transforms/registry"
 
 function makeCtx(adapter: string, body: any = {}) {
   return createRequestContext({
@@ -229,3 +232,72 @@ describe("Passthrough (LiteLLM) transform parity", () => {
     expect([...ctx.blockedTools]).toEqual([...passthroughAdapter.getBlockedBuiltinTools()])
   })
 })
+
+// The Claude Code CLI drives its own tool loop. If registry.ts has no entry for
+// adapter "claude-code" (or the transform's `adapters` array omits it), the SDK
+// runs the client's task internally on the proxy host with built-ins unblocked
+// — every Bash/Edit executes twice, once per side. Same class as #546.
+describe("Claude Code transform parity", () => {
+  let savedMP: string | undefined
+  let savedCP: string | undefined
+  beforeEach(() => {
+    savedMP = process.env.MERIDIAN_PASSTHROUGH
+    savedCP = process.env.CLAUDE_PROXY_PASSTHROUGH
+    delete process.env.MERIDIAN_PASSTHROUGH
+    delete process.env.CLAUDE_PROXY_PASSTHROUGH
+  })
+  afterEach(() => {
+    if (savedMP !== undefined) process.env.MERIDIAN_PASSTHROUGH = savedMP
+    else delete process.env.MERIDIAN_PASSTHROUGH
+    if (savedCP !== undefined) process.env.CLAUDE_PROXY_PASSTHROUGH = savedCP
+    else delete process.env.CLAUDE_PROXY_PASSTHROUGH
+  })
+
+  it("is registered under the adapter's own name", () => {
+    expect(getAdapterTransforms(claudeCodeAdapter.name)).toBe(claudeCodeTransforms)
+  })
+
+  it("matches blockedTools", () => {
+    const ctx = runTransformHook(claudeCodeTransforms, "onRequest", makeCtx("claude-code"), "claude-code")
+    expect([...ctx.blockedTools]).toEqual([...claudeCodeAdapter.getBlockedBuiltinTools()])
+    expect(ctx.blockedTools.length).toBeGreaterThan(0)
+  })
+
+  it("matches incompatibleTools and allowedMcpTools", () => {
+    const ctx = runTransformHook(claudeCodeTransforms, "onRequest", makeCtx("claude-code"), "claude-code")
+    expect([...ctx.incompatibleTools]).toEqual([...claudeCodeAdapter.getAgentIncompatibleTools()])
+    expect([...ctx.allowedMcpTools]).toEqual([...claudeCodeAdapter.getAllowedMcpTools()])
+  })
+
+  it("matches coreToolNames (PascalCase, not OpenCode's lowercase)", () => {
+    const ctx = runTransformHook(claudeCodeTransforms, "onRequest", makeCtx("claude-code"), "claude-code")
+    expect([...ctx.coreToolNames!]).toEqual([...claudeCodeAdapter.getCoreToolNames!()])
+  })
+
+  it("matches passthrough (default on)", () => {
+    const ctx = runTransformHook(claudeCodeTransforms, "onRequest", makeCtx("claude-code"), "claude-code")
+    expect(ctx.passthrough).toBe(claudeCodeAdapter.usesPassthrough!())
+    expect(ctx.passthrough).toBe(true)
+  })
+
+  it("matches passthrough (env off → false)", () => {
+    process.env.MERIDIAN_PASSTHROUGH = "0"
+    const ctx = runTransformHook(claudeCodeTransforms, "onRequest", makeCtx("claude-code"), "claude-code")
+    expect(ctx.passthrough).toBe(claudeCodeAdapter.usesPassthrough!())
+    expect(ctx.passthrough).toBe(false)
+  })
+
+  it("matches supportsThinking and shouldTrackFileChanges", () => {
+    const ctx = runTransformHook(claudeCodeTransforms, "onRequest", makeCtx("claude-code"), "claude-code")
+    expect(ctx.supportsThinking).toBe(claudeCodeAdapter.supportsThinking!())
+    expect(ctx.shouldTrackFileChanges).toBe(claudeCodeAdapter.shouldTrackFileChanges!())
+  })
+
+  it("matches file change extraction for Edit and Bash", () => {
+    const ctx = runTransformHook(claudeCodeTransforms, "onRequest", makeCtx("claude-code"), "claude-code")
+    expect(ctx.extractFileChangesFromToolUse!("Edit", { file_path: "/a.ts" }))
+      .toEqual(claudeCodeAdapter.extractFileChangesFromToolUse!("Edit", { file_path: "/a.ts" }))
+    expect(ctx.extractFileChangesFromToolUse!("Bash", { command: "echo hi > /tmp/a" }))
+      .toEqual(claudeCodeAdapter.extractFileChangesFromToolUse!("Bash", { command: "echo hi > /tmp/a" }))
+  })
+})
diff --git a/src/proxy/transforms/claudecode.ts b/src/proxy/transforms/claudecode.ts
new file mode 100644
index 00000000..095a74f2
--- /dev/null
+++ b/src/proxy/transforms/claudecode.ts
@@ -0,0 +1,58 @@
+import type { Transform, RequestContext } from "../transform"
+import { extractFileChangesFromBash, type FileChange } from "../fileChanges"
+import { BLOCKED_BUILTIN_TOOLS, CLAUDE_CODE_ONLY_TOOLS, ALLOWED_MCP_TOOLS } from "../tools"
+import { resolvePassthrough } from "../../env"
+
+/**
+ * Claude Code transform — supplies the SDK tool config at request time.
+ *
+ * server.ts reads `pipelineCtx.*`, never the adapter methods, so without an
+ * entry here a Claude Code client gets the createRequestContext defaults:
+ * `blockedTools: []` and `passthrough: undefined`. That means the SDK
+ * subprocess runs the client's task with its own built-in Read/Write/Bash on
+ * the proxy host while the client executes the same tool calls locally —
+ * every side effect happens twice (#546, same failure mode as OpenCode's).
+ *
+ * Values mirror claudeCodeAdapter (adapters/claudecode.ts); the parity tests
+ * hold the two in sync. Core tool names are PascalCase here — Claude Code's
+ * toolkit is Read/Write/Edit/Bash/Glob/Grep, not OpenCode's lowercase names.
+ */
+export const claudeCodeTransforms: Transform[] = [
+  {
+    name: "claudecode-core",
+    adapters: ["claude-code"],
+
+    onRequest(ctx: RequestContext): RequestContext {
+      const extractFileChangesFromToolUse = (toolName: string, toolInput: unknown): FileChange[] => {
+        const input = toolInput as Record<string, unknown> | null | undefined
+        const filePath = input?.file_path ?? input?.filePath ?? input?.path
+        const lowerName = toolName.toLowerCase()
+        if (lowerName === "write" && filePath) {
+          return [{ operation: "wrote", path: String(filePath) }]
+        }
+        if ((lowerName === "edit" || lowerName === "multiedit") && filePath) {
+          return [{ operation: "edited", path: String(filePath) }]
+        }
+        if (lowerName === "bash" && input?.command) {
+          return extractFileChangesFromBash(String(input.command))
+        }
+        return []
+      }
+
+      return {
+        ...ctx,
+        blockedTools: BLOCKED_BUILTIN_TOOLS,
+        incompatibleTools: CLAUDE_CODE_ONLY_TOOLS,
+        allowedMcpTools: ALLOWED_MCP_TOOLS,
+        coreToolNames: ["Read", "Write", "Edit", "Bash", "Glob", "Grep"],
+        // Claude Code owns tool execution client-side. Mirrors
+        // claudeCodeAdapter.usesPassthrough().
+        passthrough: resolvePassthrough(true),
+        supportsThinking: true,
+        // Claude Code surfaces its own file edits; don't duplicate them.
+        shouldTrackFileChanges: false,
+        extractFileChangesFromToolUse,
+      }
+    },
+  },
+]
diff --git a/src/proxy/transforms/registry.ts b/src/proxy/transforms/registry.ts
index fe63a329..06c8b241 100644
--- a/src/proxy/transforms/registry.ts
+++ b/src/proxy/transforms/registry.ts
@@ -7,6 +7,7 @@ import { forgeCodeTransforms } from "./forgecode"
 import { passthroughTransforms } from "./passthrough"
 import { cherryTransforms } from "./cherry"
 import { codexTransforms } from "./codex"
+import { claudeCodeTransforms } from "./claudecode"
 
 const ADAPTER_TRANSFORMS: Record<string, readonly Transform[]> = {
   opencode: openCodeTransforms,
@@ -16,6 +17,10 @@ const ADAPTER_TRANSFORMS: Record<string, readonly Transform[]> = {
   forgecode: forgeCodeTransforms,
   passthrough: passthroughTransforms,
   cherry: cherryTransforms,
+  // Keyed by adapter.name ("claude-code", not "claudecode"). Without this the
+  // Claude Code CLI falls through to the empty default — built-ins unblocked,
+  // passthrough off — and the SDK re-executes every tool call on the proxy host.
+  "claude-code": claudeCodeTransforms,
   // The OpenAI-compatible endpoint reuses OpenCode's transforms verbatim so
   // tool/passthrough behaviour is identical; only the preset default differs
   // (see sdkFeatures.ADAPTER_DEFAULTS.openai).