diff --git a/instructions-rework.ts b/instructions-rework.ts
deleted file mode 100644
index 10a3b52a1a..0000000000
--- a/instructions-rework.ts
+++ /dev/null
@@ -1,35 +0,0 @@
-import { searchSignature } from "./packages/codemode/src"
-import { CodeModeCatalog } from "./packages/core/src/codemode/catalog"
-
-const prompt = (catalog: CodeModeCatalog.Summary, hasMoreTools: boolean) => {
-  return `Run JavaScript to orchestrate tool calls and compose their results. Imports, filesystem access, and timers are unavailable. Do not use \`fetch\`; all API calls go through \`tools\`.
-
-Prefer an explicit \`return\`; if omitted, the final top-level expression becomes the result. Await tool calls before returning; any calls still pending when execution ends are interrupted. Run independent calls concurrently with \`Promise.all\`.
-
-Do not infer or normalize tool names; use only the exact signatures shown below${hasMoreTools ? " or returned by `search`" : ""}, preserving bracket notation such as \`tools.<namespace>["tool-name"](input)\`.${hasMoreTools ? `
-
-## Search
-
-Only some tool signatures are shown. Use \`search\` to discover exact paths and signatures for additional tools:
-
-- ${searchSignature}` : ""}
-
-## Available tools`
-}
-
-export function render(catalog: CodeModeCatalog.Summary) {
-  const hasMoreTools = true
-  const tools = catalog.namespaces.flatMap((namespace) => {
-    const count = namespace.count === 1 ? "1 tool" : `${namespace.count} tools`
-    const label = (() => {
-      if (namespace.entries.length === namespace.count) return count
-      if (namespace.entries.length === 0) return `${count}, none shown`
-      return `${count}, ${namespace.entries.length} shown`
-    })()
-    return [`- ${namespace.name} (${label})`, ...namespace.entries.map((entry) => entry.line)]
-  })
-
-  return `${prompt(catalog, hasMoreTools)}
-
-${tools.join("\n")}`
-}
diff --git a/packages/codemode/src/tool-runtime.ts b/packages/codemode/src/tool-runtime.ts
index 598d133eb8..4af3fd5a29 100644
--- a/packages/codemode/src/tool-runtime.ts
+++ b/packages/codemode/src/tool-runtime.ts
@@ -463,7 +463,7 @@ const resolve = <R>(root: ToolNode<R>, path: ReadonlyArray<string>): Tool<R> =>
   const node = lookup(root, segments)
   if (node === undefined) {
     throw new ToolRuntimeError("UnknownTool", `Unknown tool '${segments.join(".")}'.`, [
-      "Use search({ query }) to find available described tools.",
+      "The tool may have been removed or renamed. Use search to find available tools.",
     ])
   }
   if (node.tool === undefined) {
@@ -536,7 +536,11 @@ export const make = <R>(
       const input = yield* Effect.try({
         try: () => decodeToolInput(tool, externalArgs[0]),
         catch: (cause) =>
-          new ToolRuntimeError("InvalidToolInput", `Invalid input for tool '${name}': ${String(cause)}`),
+          new ToolRuntimeError(
+            "InvalidToolInput",
+            `Invalid input for tool '${name}': ${String(cause)}`,
+            name === "search" ? [] : ["The signature may have changed. Use search to get the current signature."],
+          ),
       })
       const index = yield* recordAndObserve(name, input)
       return yield* observeEnd(
diff --git a/packages/codemode/test/tool-paths.test.ts b/packages/codemode/test/tool-paths.test.ts
index 38ef4c2850..6041ff997b 100644
--- a/packages/codemode/test/tool-paths.test.ts
+++ b/packages/codemode/test/tool-paths.test.ts
@@ -85,6 +85,9 @@ describe("callable namespaces", () => {
     const diagnostic = await failure(runtime, `return await tools.issues.missing({})`)
     expect(diagnostic.kind).toBe("UnknownTool")
     expect(diagnostic.message).toContain("Unknown tool 'issues.missing'")
+    expect(diagnostic.suggestions).toEqual([
+      "The tool may have been removed or renamed. Use search to find available tools.",
+    ])
   })
 
   test("a namespace without its own tool stays non-callable", async () => {
@@ -95,6 +98,31 @@ describe("callable namespaces", () => {
   })
 })
 
+describe("tool input diagnostics", () => {
+  const runtime = CodeMode.make({
+    tools: {
+      "notes.echo": Tool.make({
+        description: "Echo text",
+        input: Schema.Struct({ text: Schema.String }),
+        output: Schema.String,
+        execute: ({ text }) => Effect.succeed(text),
+      }),
+    },
+  })
+
+  test("a schema mismatch suggests searching for the current signature", async () => {
+    const diagnostic = await failure(runtime, `return await tools.notes.echo({ message: "hello" })`)
+    expect(diagnostic.kind).toBe("InvalidToolInput")
+    expect(diagnostic.suggestions).toEqual(["The signature may have changed. Use search to get the current signature."])
+  })
+
+  test("a wrong argument count keeps the existing error without a stale-signature hint", async () => {
+    const diagnostic = await failure(runtime, `return await tools.notes.echo()`)
+    expect(diagnostic.kind).toBe("InvalidToolInput")
+    expect(diagnostic.suggestions).toBeUndefined()
+  })
+})
+
 describe("blocked member names on tool paths", () => {
   const runtime = CodeMode.make({
     tools: {
diff --git a/packages/core/src/codemode/instructions.ts b/packages/core/src/codemode/instructions.ts
index 33bbe57c59..d12869daa1 100644
--- a/packages/core/src/codemode/instructions.ts
+++ b/packages/core/src/codemode/instructions.ts
@@ -8,106 +8,44 @@ import { CodeMode } from "../codemode"
 import { Instructions } from "../instructions/index"
 import { CodeModeCatalog } from "./catalog"
 
-const completeWorkflow = `## Workflow
+// prettier-ignore
+const prompt = (hasMoreTools: boolean) => `Run JavaScript to orchestrate tool calls and compose their results. Imports, filesystem access, and timers are unavailable. Do not use \`fetch\`; all API calls go through \`tools\`.
 
-1. Pick a tool from the list under \`## Available tools\` - each line is the exact call signature; use it as-is rather than guessing segments.
-2. Call it using the exact signature shown: \`const result = await tools.<namespace>.<tool>(input)\`; bracket notation and quotes are part of the path.
-3. Return only the fields you need from structured results; narrow unknown results before reading fields, and avoid returning large raw payloads.`
+Prefer an explicit \`return\`; if omitted, the final top-level expression becomes the result. Await tool calls before returning; any calls still pending when execution ends are interrupted. Run independent calls concurrently with \`Promise.all\`.
 
-const partialWorkflow = `## Workflow
+Do not infer or normalize tool names; use only the exact signatures shown below${hasMoreTools ? " or returned by `search`" : ""}, preserving bracket notation such as \`tools.<namespace>["tool-name"](input)\`.${hasMoreTools ? `
 
-1. If needed, discover tools with the built-in search function: \`return search({ query: "<intent + key nouns>" })\`.
-2. In the next execution, copy a returned path exactly, call it, and return only the needed fields.`
+## Search
 
-const language = `## Language
+Only some tool signatures are shown. Use \`search\` to discover exact paths and signatures for additional tools:
 
-Use common JavaScript data operations, functions, control flow, selected standard-library methods, and awaited tool calls. Built-ins include Date, RegExp, Map, Set, URL, URLSearchParams, and URI encoding helpers.
-Modules/imports, classes, timers, fetch, eval, prototype access, and unlisted methods are unavailable. Use tools for external operations. Use await with try/catch.
-Prefer explicit \`return\`; otherwise only the final top-level expression becomes the result.
-Dates and URLs serialize to strings at data boundaries; Map/Set/RegExp/URLSearchParams serialize to \`{}\`.`
+- ${searchSignature}` : ""}
+
+## Available tools`
 
 export function render(catalog: CodeModeCatalog.Summary) {
-  const complete = catalog.shown === catalog.total
-  const sections: Array<string> = []
+  if (catalog.total === 0) return "No tools are currently available."
 
-  if (catalog.total === 0) {
-    sections.push("This is a restricted JavaScript language for calling tools, not a general-purpose runtime.")
-  } else {
-    const availability = (() => {
-      if (complete) return "listed below"
-      return "listed or searchable below"
-    })()
-    sections.push(
-      `This is a restricted JavaScript language for calling tools, not a general-purpose runtime. Inside the confined interpreter, \`tools\` contains the tools ${availability}; surrounding agent tools are not available.\nDo not infer or normalize tool names; use only exact signatures shown below or returned by search.`,
-    )
+  const tools = catalog.namespaces.flatMap((namespace) => {
+    const count = namespace.count === 1 ? "1 tool" : `${namespace.count} tools`
+    const label =
+      namespace.entries.length === namespace.count
+        ? count
+        : namespace.entries.length === 0
+          ? `${count}, none shown`
+          : `${count}, ${namespace.entries.length} shown`
+    return [`- ${namespace.name} (${label})`, ...namespace.entries.map((entry) => entry.line)]
+  })
 
-    if (complete) sections.push(completeWorkflow)
-    if (!complete) sections.push(partialWorkflow)
+  return `${prompt(catalog.shown < catalog.total)}
 
-    const availabilityRule = (() => {
-      if (complete) return "- Only tools listed here are available; surrounding agent tools are not implicitly exposed."
-      return "- Only tools listed here or returned by the built-in `search` function are available; surrounding agent tools are not implicitly exposed."
-    })()
-    const rules = [
-      "## Rules",
-      "",
-      availabilityRule,
-      "- Filter, aggregate, and transform collections in code - never return them raw or call a tool per item across messages.",
-      "- A result typed `Promise<unknown>` may be structured data or text. Before reading fields, check that it is a non-null object and not an array; otherwise handle the returned text or primitive directly.",
-      '- Run independent calls in parallel: `await Promise.all(items.map((item) => tools.<namespace>.<tool>(item)))`, or use `tools.<namespace>["tool-name"](item)` when the listed signature uses bracket notation.',
-      "- Execution ends when the program returns; pending promises are interrupted, so await every call whose completion matters.",
-      "- `Object.keys(tools)` lists namespaces; `Object.keys(tools.<namespace>)` lists its tools; `for...in` works on both.",
-    ]
-    if (!complete) {
-      rules.push(
-        '- Browse one namespace: `search({ query: "", namespace: "<name>" })`.',
-        "- If search returns `next`, repeat the same search with `offset: next.offset`.",
-      )
-    }
-    sections.push(rules.join("\n"))
-  }
-
-  sections.push(language)
-
-  if (catalog.total === 0) {
-    sections.push("No tools are currently available.")
-    return sections.join("\n\n")
-  }
-
-  const tools: Array<string> = []
-  if (complete) {
-    tools.push("## Available tools (COMPLETE list - every tool is shown below with its full call signature)", "")
-  } else {
-    tools.push(
-      `## Available tools (PARTIAL - ${catalog.shown} of ${catalog.total} shown; find the rest with search(...))`,
-      "",
-    )
-  }
-
-  for (const namespace of catalog.namespaces) {
-    const count = (() => {
-      if (namespace.count === 1) return "1 tool"
-      return `${namespace.count} tools`
-    })()
-    const label = (() => {
-      if (namespace.entries.length === namespace.count) return count
-      if (namespace.entries.length === 0) return `${count}, none shown`
-      return `${count}, ${namespace.entries.length} shown`
-    })()
-    tools.push(`- ${namespace.name} (${label})`, ...namespace.entries.map((entry) => entry.line))
-  }
-
-  if (!complete) tools.push("", "Search returns complete callable signatures:", `- ${searchSignature}`)
-  sections.push(tools.join("\n"))
-
-  return sections.join("\n\n")
+${tools.join("\n")}`
 }
 
 export function update(previous: CodeModeCatalog.Summary, current: CodeModeCatalog.Summary) {
-  const full = [
-    "The Code Mode tool catalog has changed. This catalog supersedes the previous Code Mode tool catalog.",
-    render(current),
-  ].join("\n\n")
+  const full = `The Code Mode tool catalog has changed. This catalog supersedes the previous Code Mode tool catalog.
+
+${render(current)}`
   const previousComplete = previous.shown === previous.total
   const currentComplete = current.shown === current.total
   if (previousComplete !== currentComplete) return full
@@ -162,9 +100,10 @@ export function update(previous: CodeModeCatalog.Summary, current: CodeModeCatal
   const parts = ["The Code Mode tool catalog has changed."]
   if (diff.added.length > 0) {
     parts.push(
-      ["New tools are available in addition to those previously listed:", ...diff.added.map((entry) => entry.line)].join(
-        "\n",
-      ),
+      [
+        "New tools are available in addition to those previously listed:",
+        ...diff.added.map((entry) => entry.line),
+      ].join("\n"),
     )
   }
   if (diff.changed.length > 0) {
@@ -200,9 +139,7 @@ const layer = Layer.effect(
 
     return Service.of({
       load: Effect.fn("CodeModeInstructions.load")(function* (selection) {
-        const entries = selection.info
-          ? ((yield* codeMode.materialize(selection.info.permissions)).catalog ?? [])
-          : []
+        const entries = selection.info ? ((yield* codeMode.materialize(selection.info.permissions)).catalog ?? []) : []
         const catalog = CodeModeCatalog.summarize(entries)
         return Instructions.make<CodeModeCatalog.Summary>({
           key: Instructions.Key.make("core/codemode"),
diff --git a/packages/core/test/codemode/catalog.test.ts b/packages/core/test/codemode/catalog.test.ts
index 9cef26e170..0cf0809d13 100644
--- a/packages/core/test/codemode/catalog.test.ts
+++ b/packages/core/test/codemode/catalog.test.ts
@@ -22,10 +22,7 @@ const update = (
   current: ReadonlyArray<CodeModeCatalog.Entry>,
   budget?: number,
 ) =>
-  CodeModeInstructions.update(
-    CodeModeCatalog.summarize(previous, budget),
-    CodeModeCatalog.summarize(current, budget),
-  )
+  CodeModeInstructions.update(CodeModeCatalog.summarize(previous, budget), CodeModeCatalog.summarize(current, budget))
 
 describe("CodeModeCatalog.summarize", () => {
   test("retains namespace inventory without retaining tools outside the inline budget", () => {
@@ -63,62 +60,37 @@ describe("CodeModeCatalog.summarize", () => {
 })
 
 describe("CodeModeInstructions.render", () => {
-  test("inlines complete catalogs with markdown sections and placeholder-only call forms", () => {
+  test("inlines complete catalogs without search guidance", () => {
     const instructions = render([lookup])
-    expect(instructions).toContain("## Available tools (COMPLETE list")
+    expect(instructions).toContain("## Available tools")
     expect(instructions).toContain("- orders (1 tool)")
     expect(instructions).toContain(`  - ${lookup.signature} // Look up an order by ID`)
-    expect(instructions).not.toContain("search(")
-
-    expect(instructions).toContain("## Workflow")
-    expect(instructions).toContain("## Rules")
-    expect(instructions).toContain("## Language")
-    expect(instructions.indexOf("## Workflow")).toBeLessThan(instructions.indexOf("## Rules"))
-    expect(instructions.indexOf("## Rules")).toBeLessThan(instructions.indexOf("## Language"))
-    expect(instructions.indexOf("## Language")).toBeLessThan(instructions.indexOf("\n## Available tools (COMPLETE"))
+    expect(instructions).not.toContain("## Search")
     expect(instructions).toContain("Do not infer or normalize tool names")
-    expect(instructions).toContain("bracket notation and quotes are part of the path")
-    expect(instructions).toContain("surrounding agent tools are not available")
-    expect(instructions).toContain("Only tools listed here are available")
-    expect(instructions).toContain("`const result = await tools.<namespace>.<tool>(input)`")
-    expect(instructions).toContain("check that it is a non-null object and not an array")
-    expect(instructions).not.toContain("tools.orders.lookup({")
-    expect(instructions).toContain("1. Pick a tool from the list under `## Available tools`")
-    expect(instructions).not.toContain("Browse one namespace")
+    expect(instructions).toContain('`tools.<namespace>["tool-name"](input)`')
   })
 
-  test("describes the restricted runtime without overclaiming", () => {
+  test("describes the runtime and execution lifecycle concisely", () => {
     const instructions = render([lookup])
-    expect(instructions).toContain("restricted JavaScript language for calling tools")
-    expect(instructions).toContain("not a general-purpose runtime")
-    for (const missing of ["Modules/imports", "classes", "fetch"]) {
-      expect(instructions).toContain(missing)
-    }
-    // Generators are supported by the interpreter and must not be listed as unavailable.
-    expect(instructions).not.toContain("generators")
-    expect(instructions).toContain("URL, URLSearchParams, and URI encoding helpers")
-    expect(instructions).toContain("Use tools for external operations")
+    expect(instructions).toContain("Run JavaScript to orchestrate tool calls and compose their results.")
+    expect(instructions).toContain("Imports, filesystem access, and timers are unavailable.")
+    expect(instructions).toContain("Do not use `fetch`; all API calls go through `tools`.")
     expect(instructions).toContain(
-      "Prefer explicit `return`; otherwise only the final top-level expression becomes the result.",
-    )
-    expect(instructions).toContain(
-      "Dates and URLs serialize to strings at data boundaries; Map/Set/RegExp/URLSearchParams serialize to `{}`.",
+      "Prefer an explicit `return`; if omitted, the final top-level expression becomes the result.",
     )
+    expect(instructions).toContain("any calls still pending when execution ends are interrupted")
+    expect(instructions).toContain("Run independent calls concurrently with `Promise.all`.")
   })
 
-  test("switches to search-first guidance when the catalog exceeds the budget", () => {
+  test("adds search guidance when the catalog exceeds the budget", () => {
     const partial = render([lookup], 0)
-    expect(partial).toContain("## Available tools (PARTIAL - 0 of 1 shown; find the rest with search(...))")
+    expect(partial).toContain("## Available tools")
     expect(partial).toContain("- orders (1 tool, none shown)")
-    expect(partial).toContain(
-      '1. If needed, discover tools with the built-in search function: `return search({ query: "<intent + key nouns>" })`.',
-    )
-    expect(partial).toContain("In the next execution, copy a returned path exactly")
-    expect(partial).toContain("Only tools listed here or returned by the built-in `search` function")
-    expect(partial).toContain('- Browse one namespace: `search({ query: "", namespace: "<name>" })`.')
-    expect(partial).toContain("repeat the same search with `offset: next.offset`")
-    expect(partial).toContain("Search returns complete callable signatures:\n- search(input: {")
+    expect(partial).toContain("## Search")
+    expect(partial).toContain("Only some tool signatures are shown.")
+    expect(partial).toContain("- search(input: {")
     expect(partial).toContain("  limit?: number,\n  offset?: number,")
+    expect(partial).toContain("or returned by `search`")
     expect(partial).not.toContain("tools.orders.lookup(input:")
   })
 
@@ -133,7 +105,7 @@ describe("CodeModeInstructions.render", () => {
     // Round 1 places alpha.cheap and beta.cheap; in round 2 alpha.expensive does not fit,
     // which marks only alpha done - it must NOT prevent other namespaces from inlining.
     const instructions = render([cheapAlpha, expensive, cheapBeta], 40)
-    expect(instructions).toContain("## Available tools (PARTIAL - 2 of 3 shown; find the rest with search(...))")
+    expect(instructions).toContain("## Search")
     expect(instructions).toContain("- alpha (2 tools, 1 shown)")
     expect(instructions).toContain(`  - ${cheapAlpha.signature} // Cheap`)
     expect(instructions).not.toContain("tools.alpha.expensive(")
@@ -148,18 +120,12 @@ describe("CodeModeInstructions.render", () => {
       `tools.records.lookup(input: {\n  /** ${"A detailed identifier description. ".repeat(20).trim()} */\n  id: string,\n}): Promise<string>`,
     )
     const instructions = render([documented], 40)
-    expect(instructions).toContain("## Available tools (PARTIAL - 0 of 1 shown; find the rest with search(...))")
+    expect(instructions).toContain("- records (1 tool, none shown)")
     expect(instructions).not.toContain("tools.records.lookup(input:")
   })
 
-  test("renders the no-tools notice with minimal sections for an empty catalog", () => {
-    const instructions = render([])
-    expect(instructions).toContain("No tools are currently available.")
-    expect(instructions).toContain("## Language")
-    expect(instructions).not.toContain("## Available tools")
-    expect(instructions).not.toContain("## Workflow")
-    expect(instructions).not.toContain("## Rules")
-    expect(instructions).not.toContain("search(")
+  test("renders only the no-tools notice for an empty catalog", () => {
+    expect(render([])).toBe("No tools are currently available.")
   })
 })
 
@@ -193,14 +159,16 @@ describe("CodeModeInstructions.update", () => {
     expect(text).toContain(
       "The Code Mode tool catalog has changed. This catalog supersedes the previous Code Mode tool catalog.",
     )
-    expect(text).toContain("## Available tools (PARTIAL")
+    expect(text).toContain("## Search")
+    expect(text).toContain("## Available tools")
   })
 
   test("falls back to full replacement when the delta is larger than the catalog", () => {
     const previous = Array.from({ length: 200 }, (_, index) => entry(`bulk.tool${index}`, `Tool ${index}`))
     const text = update([...previous, echo], [echo])
     expect(text).toContain("This catalog supersedes the previous Code Mode tool catalog.")
-    expect(text).toContain("## Available tools (COMPLETE list")
+    expect(text).toContain("## Available tools")
+    expect(text).not.toContain("## Search")
     expect(text).not.toContain("must not be called")
   })
 
diff --git a/packages/core/test/codemode/instructions.test.ts b/packages/core/test/codemode/instructions.test.ts
index 187b2ac156..9e7ee58553 100644
--- a/packages/core/test/codemode/instructions.test.ts
+++ b/packages/core/test/codemode/instructions.test.ts
@@ -38,7 +38,8 @@ describe("CodeModeInstructions", () => {
     return Effect.gen(function* () {
       const instructions = yield* CodeModeInstructions.Service
       const initialized = yield* instructions.load({ id: agent.id, info: agent }).pipe(Effect.flatMap(readInitial))
-      expect(initialized.text).toContain("## Available tools (COMPLETE list")
+      expect(initialized.text).toContain("## Available tools")
+      expect(initialized.text).not.toContain("## Search")
       expect(initialized.text).toContain(`  - ${echo.signature} // Echo text`)
 
       catalog = [echo, lookup]