diff --git a/packages/app/src/composer/history/entry.test.ts b/packages/app/src/composer/history/entry.test.ts
index 32ae31172a0..5b747cc7ce8 100644
--- a/packages/app/src/composer/history/entry.test.ts
+++ b/packages/app/src/composer/history/entry.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test"
 import type { Prompt } from "@/composer/state"
-import { prependHistoryEntry, type PromptHistoryComment } from "./entry"
+import { prependHistoryEntry, removeHistoryEntry, type PromptHistoryComment } from "./entry"
 import { Schema } from "effect"
 import { PromptHistoryState } from "../schema"
 import { Persistence } from "@/runtime/persistence/schema"
@@ -36,6 +36,24 @@ describe("Composer history", () => {
     expect(dedupedComments).toBe(commentsOnly)
   })
 
+  test("removeHistoryEntry drops the entry recorded for a prompt and leaves others alone", () => {
+    const image: Prompt = [
+      { type: "text", content: "look", start: 0, end: 4 },
+      { type: "image", id: "img", filename: "big.png", mime: "image/png", blob: { id: "hash", url: "" } },
+    ]
+    const entries = prependHistoryEntry(prependHistoryEntry([], text("earlier")), image, [comment("c1")])
+    expect(entries).toHaveLength(2)
+
+    const untouched = removeHistoryEntry(entries, text("never sent"))
+    expect(untouched).toBe(entries)
+
+    const withoutComments = removeHistoryEntry(entries, image)
+    expect(withoutComments).toBe(entries)
+
+    const removed = removeHistoryEntry(entries, image, [comment("c1")])
+    expect(removed).toEqual(prependHistoryEntry([], text("earlier")))
+  })
+
   test("insertion isolates canonical entries from source mutations", () => {
     const prompt: Prompt = [
       {
diff --git a/packages/app/src/composer/history/entry.ts b/packages/app/src/composer/history/entry.ts
index 1233cf2a278..0c76c01d29f 100644
--- a/packages/app/src/composer/history/entry.ts
+++ b/packages/app/src/composer/history/entry.ts
@@ -48,6 +48,18 @@ export function prependHistoryEntry(
   return [entry, ...entries].slice(0, max)
 }
 
+// A send that failed puts its prompt back in the composer, so the entry recorded for it would
+// only duplicate the draft and keep its attachments referenced for as long as history holds it.
+export function removeHistoryEntry(
+  entries: PromptHistoryStoredEntry[],
+  prompt: Prompt,
+  comments: PromptHistoryComment[] = [],
+) {
+  const entry = { prompt, comments } satisfies PromptHistoryEntry
+  const next = entries.filter((item) => !isPromptEqual(item, entry))
+  return next.length === entries.length ? entries : next
+}
+
 function isCommentEqual(commentA: PromptHistoryComment, commentB: PromptHistoryComment) {
   return (
     commentA.path === commentB.path &&
diff --git a/packages/app/src/composer/history/store.ts b/packages/app/src/composer/history/store.ts
index f29ab3de3ea..d72314b0b30 100644
--- a/packages/app/src/composer/history/store.ts
+++ b/packages/app/src/composer/history/store.ts
@@ -4,6 +4,7 @@ import { Persist, persisted } from "@/runtime/persistence/storage"
 import {
   clonePromptHistoryComments,
   prependHistoryEntry,
+  removeHistoryEntry,
   type PromptHistoryComment,
   type PromptHistoryStoredEntry,
 } from "./entry"
@@ -13,6 +14,7 @@ import { PromptHistoryState } from "../schema"
 export type ComposerHistoryStore = {
   entries: (mode: "normal" | "shell") => PromptHistoryStoredEntry[]
   add: (prompt: Prompt, mode: "normal" | "shell", comments: PromptHistoryComment[]) => void
+  remove: (prompt: Prompt, mode: "normal" | "shell", comments: PromptHistoryComment[]) => void
 }
 
 type PromptHistoryState = typeof PromptHistoryState.Type
@@ -32,6 +34,13 @@ function createComposerHistoryStore(
       if (next === current.entries) return
       setCurrent("entries", next)
     },
+    remove(prompt, mode, comments) {
+      const current = mode === "shell" ? shell : normal
+      const setCurrent = mode === "shell" ? setShell : setNormal
+      const next = removeHistoryEntry(current.entries, prompt, comments)
+      if (next === current.entries) return
+      setCurrent("entries", next)
+    },
   }
 }
 
@@ -56,5 +65,12 @@ export function createComposerHistory() {
       const metadata = clonePromptHistoryComments(comments)
       void ready.then(() => history.add(saved, mode, metadata))
     },
+    remove(prompt: Prompt, mode: "normal" | "shell", comments: PromptHistoryComment[]) {
+      const ready = mode === "shell" ? shellInit : normalInit
+      if (!(ready instanceof Promise)) return history.remove(prompt, mode, comments)
+      const saved = clonePrompt(prompt)
+      const metadata = clonePromptHistoryComments(comments)
+      void ready.then(() => history.remove(saved, mode, metadata))
+    },
   }
 }
diff --git a/packages/app/src/composer/model.ts b/packages/app/src/composer/model.ts
index 108a7d6443b..c785e95da7c 100644
--- a/packages/app/src/composer/model.ts
+++ b/packages/app/src/composer/model.ts
@@ -264,6 +264,7 @@ export function createComposerModel(adapter: ComposerAdapter, options?: { queue?
     editor: () => editor,
     queueScroll: () => requestAnimationFrame(() => editor?.scrollIntoView({ block: "nearest" })),
     addToHistory: (value, mode) => controller.addHistory(value, mode),
+    removeFromHistory: (value, mode, comments) => history.remove(value, mode, mode === "shell" ? [] : comments),
     resetHistory: () => controller.resetHistory(),
     setMode: (next) => controller.dispatch({ type: next === "shell" ? "mode.shell" : "mode.normal" }),
     closePopover: () => controller.dispatch({ type: "popover.close" }),
diff --git a/packages/app/src/composer/submit.test.ts b/packages/app/src/composer/submit.test.ts
index d100291cd1f..9db0102c368 100644
--- a/packages/app/src/composer/submit.test.ts
+++ b/packages/app/src/composer/submit.test.ts
@@ -53,6 +53,7 @@ function submitInput(
   notify = { missingSelection() {}, failed(_kind: "shell" | "command" | "prompt", _error: unknown) {} },
   mode: "normal" | "shell" = "normal",
   commands: () => readonly { name: string }[] | undefined = () => [],
+  history: string[] = [],
 ) {
   return createComposerSubmit({
     adapter,
@@ -60,7 +61,9 @@ function submitInput(
     commands,
     editor: () => undefined,
     queueScroll() {},
-    addToHistory() {},
+    addToHistory: (prompt) => history.push(`add:${prompt.map((part) => ("content" in part ? part.content : part.type)).join("")}`),
+    removeFromHistory: (prompt) =>
+      history.push(`remove:${prompt.map((part) => ("content" in part ? part.content : part.type)).join("")}`),
     resetHistory() {},
     setMode() {},
     closePopover() {},
@@ -533,12 +536,8 @@ describe("Composer submission", () => {
       missingSelection() {},
       failed: () => (attempts.length === 2 ? first.resolve() : second.resolve()),
     }
-    const submission = submitInput(
-      adapter,
-      notify,
-      "normal",
-      () => [],
-    )
+    const history: string[] = []
+    const submission = submitInput(adapter, notify, "normal", () => [], history)
 
     await submission.submit(new Event("submit"))
     await first.promise
@@ -549,6 +548,8 @@ describe("Composer submission", () => {
     expect(new Set(attempts).size).toBe(1)
     expect(statuses).toEqual(["running", "idle", "running", "idle"])
     expect(state.current()).toMatchObject([{ type: "text", content: text }])
+    // The restored prompt is the draft again, so history does not also keep it (and its attachments).
+    expect(history).toEqual([`add:${text}`, `remove:${text}`, `add:${text}`, `remove:${text}`])
   })
 
   test("forwards structured mentions to custom commands", async () => {
diff --git a/packages/app/src/composer/submit.ts b/packages/app/src/composer/submit.ts
index 31a368f886a..762fc07978a 100644
--- a/packages/app/src/composer/submit.ts
+++ b/packages/app/src/composer/submit.ts
@@ -32,6 +32,7 @@ type ComposerSubmitInput = {
   editor: () => HTMLDivElement | undefined
   queueScroll: () => void
   addToHistory: (prompt: Prompt, mode: "normal" | "shell") => void
+  removeFromHistory: (prompt: Prompt, mode: "normal" | "shell", comments: PromptHistoryComment[]) => void
   resetHistory: () => void
   setMode: (mode: "normal" | "shell") => void
   closePopover: () => void
@@ -250,6 +251,8 @@ function restoreSubmission(
 ) {
   const restored = submission.restore()
   if (!restored) return false
+  // The prompt is back in the composer; its history entry would only keep attachments referenced.
+  input.removeFromHistory(value.prompt, value.mode, comments)
   restored.target.set(restored.prompt, promptLength(restored.prompt))
   restored.target.mode.set(value.mode)
   restored.target.context.replaceComments(
diff --git a/packages/ui/src/feedback/toast/description.test.ts b/packages/ui/src/feedback/toast/description.test.ts
new file mode 100644
index 00000000000..ca1c5ce2fb0
--- /dev/null
+++ b/packages/ui/src/feedback/toast/description.test.ts
@@ -0,0 +1,20 @@
+import { describe, expect, test } from "bun:test"
+import { boundToastDescription, toastDescriptionLimit } from "./description"
+
+describe("toast description bound", () => {
+  test("keeps ordinary descriptions and the options object", () => {
+    const options = { title: "Failed", description: "Attachment exceeds the limit" }
+    expect(boundToastDescription(options)).toBe(options)
+    expect(boundToastDescription({ description: undefined })).toEqual({ description: undefined })
+  })
+
+  test("cuts a description that embeds a whole data URL", () => {
+    const description = `Attachment exceeds the limit: data:text/plain;base64,${"Q".repeat(50 * 1024 * 1024)}`
+    const bounded = boundToastDescription({ title: "Failed to send prompt", description })
+    expect(bounded.description!.length).toBe(toastDescriptionLimit + 1)
+    expect(bounded.description!.endsWith("…")).toBe(true)
+    expect(bounded.description!.startsWith("Attachment exceeds the limit: data:text/plain;base64,")).toBe(true)
+    expect(bounded.title).toBe("Failed to send prompt")
+  })
+})
+
diff --git a/packages/ui/src/feedback/toast/description.ts b/packages/ui/src/feedback/toast/description.ts
new file mode 100644
index 00000000000..eaaba104a73
--- /dev/null
+++ b/packages/ui/src/feedback/toast/description.ts
@@ -0,0 +1,9 @@
+// A toast shows a few lines; the rest of a long description would only be retained (in the dedupe
+// key, the active-toast registry and the toaster's store) for as long as the toast lives. Server
+// errors have carried a whole data URL here.
+export const toastDescriptionLimit = 2000
+
+export function boundToastDescription<T extends { description?: string }>(options: T): T {
+  if (!options.description || options.description.length <= toastDescriptionLimit) return options
+  return { ...options, description: `${options.description.slice(0, toastDescriptionLimit)}…` }
+}
diff --git a/packages/ui/src/feedback/toast/toast.tsx b/packages/ui/src/feedback/toast/toast.tsx
index 554f03b7728..cab8b7a707b 100644
--- a/packages/ui/src/feedback/toast/toast.tsx
+++ b/packages/ui/src/feedback/toast/toast.tsx
@@ -1,4 +1,5 @@
 import { Toaster, toast, type ToasterProps } from "solid-sonner"
+import { boundToastDescription } from "./description"
 import { isRTL } from "@kobalte/core/i18n"
 import type { ComponentProps, JSX } from "solid-js"
 import { createContext, onCleanup, onMount, splitProps, useContext } from "solid-js"
@@ -205,7 +206,7 @@ const activeToastByKey = new Map<string, ActiveToast>()
 const activeToastById = new Map<number, ActiveToast>()
 
 export function showToast(options: ToastOptions | string) {
-  const opts: ToastOptions = typeof options === "string" ? { description: options } : options
+  const opts = boundToastDescription(typeof options === "string" ? { description: options } : options)
   const key = JSON.stringify({
     title: opts.title,
     description: opts.description,