diff --git a/packages/core/src/session/model-request.ts b/packages/core/src/session/model-request.ts
index fab9e4c0e465..06d9ae989064 100644
--- a/packages/core/src/session/model-request.ts
+++ b/packages/core/src/session/model-request.ts
@@ -191,22 +191,31 @@ export const layer = Layer.effect(
       const messages = stepLimitReached ? [...history, Message.assistant(MAX_STEPS_PROMPT)] : history
       const toolDefinitions = tools.definitions
       const toolsByName = new Map(toolDefinitions.map((tool) => [tool.name, tool]))
+      // Object identity preserves registry provenance when a hook moves a definition to a new key.
+      const toolNamesByDefinition = new Map<object, string>()
       // Hooks may reshape available definitions but cannot advertise tools omitted by permissions or the Step limit.
+      const hookTools = Object.fromEntries(
+        toolDefinitions.map((tool) => {
+          const definition = { description: tool.description, input: { ...tool.inputSchema } }
+          toolNamesByDefinition.set(definition, tool.name)
+          return [tool.name, definition]
+        }),
+      )
       const contextEvent = yield* hooks.trigger("session", "context", {
         sessionID: session.id,
         agent: agent.id,
         model: resolved.ref,
         system,
         messages,
-        tools: Object.fromEntries(
-          toolDefinitions.map((tool) => [tool.name, { description: tool.description, input: { ...tool.inputSchema } }]),
-        ),
+        tools: hookTools,
       })
+      const executableTools = new Map<string, string>()
       const hookedTools = Object.entries(contextEvent.tools).flatMap(([name, tool]) => {
-        const registered = toolsByName.get(name)
-        return registered
-          ? [{ ...registered, description: tool.description, inputSchema: tool.input }]
-          : []
+        const registeredName = toolNamesByDefinition.get(tool)
+        const registered = registeredName ? toolsByName.get(registeredName) : undefined
+        if (!registered || !registeredName) return []
+        executableTools.set(name, registeredName)
+        return [{ ...registered, name, description: tool.description, inputSchema: tool.input }]
       })
       const request = LLM.request({
         model,
@@ -259,10 +268,14 @@ export const layer = Layer.effect(
       const executeTool: Prepared["executeTool"] = (executeInput) => {
         if (stepLimitReached)
           return new Tool.Error({ message: "Tools are disabled after the maximum agent steps" })
-        if (toolsByName.has(executeInput.call.name) && !Object.hasOwn(contextEvent.tools, executeInput.call.name))
+        const registeredName = executableTools.get(executeInput.call.name)
+        if (!registeredName && toolsByName.has(executeInput.call.name))
           return new Tool.Error({ message: `Tool is not available for this request: ${executeInput.call.name}` })
         return tools
-          .execute(executeInput)
+          .execute({
+            ...executeInput,
+            call: { ...executeInput.call, name: registeredName ?? executeInput.call.name },
+          })
           .pipe(Effect.catchCauseFilter(declineDefect, (decline) => Effect.fail(decline)))
       }
       return {
diff --git a/packages/core/test/session-runner.test.ts b/packages/core/test/session-runner.test.ts
index f7bca091004e..a82a4366afe0 100644
--- a/packages/core/test/session-runner.test.ts
+++ b/packages/core/test/session-runner.test.ts
@@ -887,6 +887,42 @@ describe("SessionRunnerLLM", () => {
     }),
   )
 
+  it.effect("advertises and executes a tool renamed by a session context hook", () =>
+    Effect.gen(function* () {
+      const session = yield* setup
+      const hooks = yield* PluginHooks.Service
+      yield* hooks.register("session", "context", (event) =>
+        Effect.sync(() => {
+          const tool = event.tools.echo
+          if (!tool) return
+          event.tools.renamed_echo = tool
+          delete event.tools.echo
+        }),
+      )
+      yield* admit(session, "Use the renamed tool")
+      yield* TestLLM.push(TestLLM.tool("call-renamed", "renamed_echo", { text: "renamed" }), [])
+
+      yield* session.resume(sessionID)
+
+      expect(requests[0]?.tools.map((tool) => tool.name)).toContain("renamed_echo")
+      expect(requests[0]?.tools.map((tool) => tool.name)).not.toContain("echo")
+      expect(executions).toEqual(["renamed"])
+      expect(yield* session.context(sessionID)).toMatchObject([
+        { type: "user", text: "Use the renamed tool" },
+        {
+          type: "assistant",
+          content: [
+            {
+              type: "tool",
+              id: "call-renamed",
+              state: { status: "completed", content: [{ type: "text", text: "renamed" }] },
+            },
+          ],
+        },
+      ])
+    }),
+  )
+
   it.effect("advertises and executes a location registered tool", () =>
     Effect.gen(function* () {
       const session = yield* setup