From ed1d659074cb83f0d5607cb682fe86604d2afcc1 Mon Sep 17 00:00:00 2001
From: Kevin Buffardi <kbuffardi@csuchico.edu>
Date: Sat, 1 Aug 2026 14:23:38 -0700
Subject: [PATCH] fix(firefox): require live terminal stdin

---
 README.md                                  |  8 +--
 docs/firefox-stdin-runtime-acceptance.md   | 25 +++----
 docs/release-playbook.md                   |  2 +-
 package.json                               |  2 +-
 scripts/e2e-buffered-stdin-ui.test.mjs     | 25 -------
 scripts/e2e-firefox-compatibility.test.mjs |  6 +-
 scripts/e2e-firefox-jspi-stdin.test.mjs    |  6 +-
 scripts/e2e-run-request.test.mjs           | 19 +-----
 scripts/e2e-terminal-stop.test.mjs         | 69 ++-----------------
 scripts/e2e-wasi-shim.test.mjs             | 66 ++----------------
 src/ui/browser-capabilities.mjs            |  6 +-
 src/ui/buffered-stdin-dialog.mjs           | 78 ----------------------
 src/ui/index.html                          | 23 -------
 src/ui/styles.css                          | 73 --------------------
 src/ui/terminal.js                         | 34 +++-------
 src/workers/compiler.worker.js             |  3 -
 src/workers/run-request.mjs                | 13 +---
 src/workers/wasi-shim.mjs                  | 20 ------
 18 files changed, 45 insertions(+), 433 deletions(-)
 delete mode 100644 scripts/e2e-buffered-stdin-ui.test.mjs
 delete mode 100644 src/ui/buffered-stdin-dialog.mjs

diff --git a/README.md b/README.md
index f4f4b11..5d8eabd 100644
--- a/README.md
+++ b/README.md
@@ -220,8 +220,8 @@ different:
 
 - compile/run, Monaco, and extension-runtime flows are supported
 - Firefox 153+ uses WebAssembly JSPI for live, line-buffered `std::cin`,
-  `std::getline`, and `scanf` input; Firefox 140–152 (or a runtime without
-  JSPI) retains the pre-supplied buffered stdin fallback (up to 256 KiB)
+  `std::getline`, and `scanf` input; Firefox runtimes without worker-side JSPI
+  cannot run stdin-reading programs
 - file open/save and folder import use fallback browser flows rather than
   Chromium File System Access APIs
 - persistent folder write-back and directory-handle session restore may be
@@ -464,7 +464,7 @@ manual/GitHub-distributed channel.
    signed artifact under `release/firefox-unlisted/`.
 5. Install the signed XPI in Firefox and complete the manual QA checklist
    in `docs/firefox-stdin-runtime-acceptance.md`, paying special attention to
-   JSPI live stdin, its buffered fallback, and the documented
+   JSPI live stdin and the documented
    workspace-persistence limitations.
 
 ### Manual release QA checklist
@@ -530,7 +530,7 @@ Copy the resulting `clang.js` and `clang.wasm` into `dist/clang/`.
   the UI.
 - **Browser scope**: Full parity targets desktop Chrome, Edge, Brave, and
   Chromium. Firefox 153+ supports live canonical (line-buffered) stdin through
-  JSPI; older supported Firefox versions use buffered stdin. This is not a raw
+  JSPI; older or no-JSPI Firefox runtimes cannot provide terminal stdin. This is not a raw
   POSIX PTY, and Firefox workspace-persistence limitations remain. Safari is
   outside the current release target.
 - **Managed browsers**: Enterprise policies that block File System Access prompts
diff --git a/docs/firefox-stdin-runtime-acceptance.md b/docs/firefox-stdin-runtime-acceptance.md
index e6ba980..3d290b4 100644
--- a/docs/firefox-stdin-runtime-acceptance.md
+++ b/docs/firefox-stdin-runtime-acceptance.md
@@ -4,10 +4,10 @@ Use this procedure to validate live JSPI terminal input from GitHub issue #55
 in a real Firefox extension context. `npm run test:browser:firefox` validates
 packaging and manifest compatibility, but does not execute a compiled program.
 
-Firefox 153+ should use live, canonical (line-buffered) input. Firefox 140–152,
-or a runtime where JSPI is unavailable, should keep the pre-supplied buffered
-fallback. Persistent folder write-back is outside this test and retains its
-documented Firefox limitations.
+Firefox 153+ with worker-side JSPI must use live, canonical (line-buffered)
+input. A Firefox runtime where JSPI is unavailable must report stdin as
+unsupported and must not open a pre-supplied-input dialog. Persistent folder
+write-back is outside this test and retains its documented Firefox limitations.
 
 ## Setup
 
@@ -55,7 +55,7 @@ int main() {
 
 1. Choose **Compile and Run**.
 2. Confirm `Name? ` appears before entering anything and that the
-   **Pre-supplied stdin** dialog does not open.
+   pre-supplied-input dialog does not open.
 3. Type `Ada`, press Enter, and confirm `Age? ` appears afterward.
 4. Type `41` and press Enter.
 5. Confirm the final line is `Hello Ada, next year 42` and the process exits
@@ -72,19 +72,14 @@ This validates two independent suspend/resume cycles and prompt ordering.
 3. Run once more and complete both inputs successfully. Confirm no input from
    either prior run appears in the new process.
 
-## Buffered fallback test
+## Unsupported-runtime test
 
 Repeat in Firefox 140–152, or in a controlled environment where the worker does
 not expose both `WebAssembly.Suspending` and `WebAssembly.promising`.
 
 1. Choose **Compile and Run**.
-2. Confirm the **Pre-supplied stdin** dialog opens.
-3. Enter `Ada`, a newline, `41`, and a final newline; then choose **Run
-   program**.
-4. Confirm the same successful final output.
-
-The fallback must not attempt message-interactive stdin merely from the Firefox
-version string or main-window capabilities.
+2. Confirm no pre-supplied-input dialog opens.
+3. Confirm the terminal reports that live stdin is unavailable and posts no run.
 
 ## Error exclusions
 
@@ -107,6 +102,6 @@ Record the following in the pull request or follow-up release evidence:
 - exact observed prompt/output ordering
 - confirmation that each input was entered only after its prompt appeared
 - Ctrl+D, Ctrl+C, and clean-rerun results
-- confirmation that the buffered dialog was absent on Firefox 153+ JSPI and
-  present in the no-JSPI fallback test
+- confirmation that no pre-supplied-input dialog exists and no-JSPI reports
+  unsupported stdin
 - confirmation that stderr and the Browser Console had no unexpected errors
diff --git a/docs/release-playbook.md b/docs/release-playbook.md
index e6a4838..c230e69 100644
--- a/docs/release-playbook.md
+++ b/docs/release-playbook.md
@@ -88,7 +88,7 @@ real Firefox desktop build:
    console/runtime errors.
 3. Compile and run the default sample program.
 4. Complete `docs/firefox-stdin-runtime-acceptance.md`: confirm Firefox 153+
-   JSPI live stdin and the older/no-JSPI buffered fallback both work without
+   JSPI live stdin works without
    SharedArrayBuffer/COOP/COEP errors.
 5. Open a local source file with Firefox's fallback picker and save changes.
 6. Import a folder, compile a multi-file project, and confirm diagnostics appear
diff --git a/package.json b/package.json
index 8cfaf64..118b91b 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,7 @@
     "lint": "eslint .",
     "build": "npm run build:webpack && npm run build:targets",
     "build:firefox": "npm run build",
-    "test:e2e": "node --experimental-detect-module --test scripts/e2e-session-persistence.test.mjs scripts/e2e-session-restore-choice.test.mjs scripts/e2e-multifile-build.test.mjs scripts/e2e-workspace-file-tracking.test.mjs scripts/e2e-terminal-mkdir.test.mjs scripts/e2e-terminal-stop.test.mjs scripts/e2e-terminal-git-removal.test.mjs scripts/e2e-terminal-stop-icon.test.mjs scripts/e2e-buffered-stdin-ui.test.mjs scripts/e2e-browser-compatibility.test.mjs scripts/e2e-firefox-compatibility.test.mjs scripts/e2e-firefox-jspi-stdin.test.mjs scripts/e2e-wasi-shim.test.mjs scripts/e2e-run-request.test.mjs scripts/e2e-release-packaging.test.mjs",
+    "test:e2e": "node --experimental-detect-module --test scripts/e2e-session-persistence.test.mjs scripts/e2e-session-restore-choice.test.mjs scripts/e2e-multifile-build.test.mjs scripts/e2e-workspace-file-tracking.test.mjs scripts/e2e-terminal-mkdir.test.mjs scripts/e2e-terminal-stop.test.mjs scripts/e2e-terminal-git-removal.test.mjs scripts/e2e-terminal-stop-icon.test.mjs scripts/e2e-browser-compatibility.test.mjs scripts/e2e-firefox-compatibility.test.mjs scripts/e2e-firefox-jspi-stdin.test.mjs scripts/e2e-wasi-shim.test.mjs scripts/e2e-run-request.test.mjs scripts/e2e-release-packaging.test.mjs",
     "test:preflight-clang": "node scripts/preflight-clang-artifacts.js",
     "test:browser:chrome": "npm run test:preflight-clang && node scripts/smoke-browser.mjs chrome",
     "test:browser:edge": "npm run test:preflight-clang && node scripts/smoke-browser.mjs edge",
diff --git a/scripts/e2e-buffered-stdin-ui.test.mjs b/scripts/e2e-buffered-stdin-ui.test.mjs
deleted file mode 100644
index ac89b73..0000000
--- a/scripts/e2e-buffered-stdin-ui.test.mjs
+++ /dev/null
@@ -1,25 +0,0 @@
-import test from 'node:test';
-import assert from 'node:assert/strict';
-import { readFile } from 'node:fs/promises';
-
-test('e2e: buffered stdin dialog has accessible controls and status feedback', async () => {
-  const html = await readFile('src/ui/index.html', 'utf8');
-  const dialog = html.match(/<dialog id="buffered-stdin-dialog"[\s\S]*?<\/dialog>/)?.[0];
-
-  assert.ok(dialog, 'buffered stdin dialog markup should exist');
-  assert.match(dialog, /aria-labelledby="buffered-stdin-title"/);
-  assert.match(dialog, /<label for="buffered-stdin-input"/);
-  assert.match(dialog, /<textarea[\s\S]*id="buffered-stdin-input"[\s\S]*aria-describedby="buffered-stdin-feedback"/);
-  assert.match(dialog, /<textarea[\s\S]*maxlength="262144"/);
-  assert.match(dialog, /id="buffered-stdin-feedback"[\s\S]*aria-live="polite"/);
-  assert.match(dialog, /<button[^>]*id="buffered-stdin-cancel"/);
-  assert.match(dialog, /<button[^>]*id="buffered-stdin-run"/);
-});
-
-test('e2e: buffered stdin dialog styles remain usable in narrow extension windows', async () => {
-  const css = await readFile('src/ui/styles.css', 'utf8');
-
-  assert.match(css, /#buffered-stdin-dialog\s*\{[\s\S]*width:\s*min\(/);
-  assert.match(css, /#buffered-stdin-input\s*\{[\s\S]*resize:\s*vertical/);
-  assert.match(css, /buffered-stdin-feedback/);
-});
diff --git a/scripts/e2e-firefox-compatibility.test.mjs b/scripts/e2e-firefox-compatibility.test.mjs
index 2057491..535f520 100644
--- a/scripts/e2e-firefox-compatibility.test.mjs
+++ b/scripts/e2e-firefox-compatibility.test.mjs
@@ -47,7 +47,7 @@ test('e2e: extracts Firefox major versions from Firefox user agents', () => {
   assert.equal(getFirefoxMajor('Chrome/126.0.0.0 Safari/537.36'), null);
 });
 
-test('e2e: Firefox compatibility report accepts supported fallback-based capabilities', () => {
+test('e2e: Firefox compatibility report identifies live stdin as unsupported without JSPI', () => {
   const report = createBrowserCompatibilityReport(firefoxLikeRoot());
   const message = formatBrowserCompatibilityMessage(report);
 
@@ -55,11 +55,11 @@ test('e2e: Firefox compatibility report accepts supported fallback-based capabil
   assert.equal(report.capabilities.browserFamily, 'firefox');
   assert.equal(report.capabilities.supportLevel, 'compatible');
   assert.equal(report.capabilities.interactiveStdin, false);
-  assert.equal(report.capabilities.stdinMode, 'buffered');
+  assert.equal(report.capabilities.stdinMode, 'unsupported');
   assert.deepEqual(report.missing, []);
   assert.ok(report.limitations.some((item) => item.key === 'limitedInteractiveStdin'));
   assert.ok(report.limitations.some((item) => item.key === 'firefoxWorkspacePersistence'));
-  assert.ok(message.includes('pre-supplied buffered stdin'));
+  assert.ok(message.includes('requires worker-side JSPI'));
   assert.ok(message.includes('Persistent folder write-back'));
 });
 
diff --git a/scripts/e2e-firefox-jspi-stdin.test.mjs b/scripts/e2e-firefox-jspi-stdin.test.mjs
index e93eefd..c9b01db 100644
--- a/scripts/e2e-firefox-jspi-stdin.test.mjs
+++ b/scripts/e2e-firefox-jspi-stdin.test.mjs
@@ -98,8 +98,8 @@ test('e2e: Firefox 153 reports JSPI potential but waits for worker confirmation'
   assert.equal(capabilities.jspi, true);
   assert.equal(capabilities.jspiPotentialInteractiveStdin, true);
   assert.equal(capabilities.interactiveStdin, false);
-  assert.equal(capabilities.stdinMode, 'buffered');
-  assert.equal(selectStdinTransport(capabilities, { jspi: false }), 'buffered');
+  assert.equal(capabilities.stdinMode, 'unsupported');
+  assert.equal(selectStdinTransport(capabilities, { jspi: false }), 'unsupported');
   assert.equal(selectStdinTransport(capabilities, { jspi: true }), 'message-jspi');
 
   const negotiatedReport = createBrowserCompatibilityReport({
@@ -142,7 +142,7 @@ test('e2e: stdin selection keeps Chromium SharedArrayBuffer first and gates olde
     firefoxMajor: 152,
     sharedBufferInteractiveStdin: false,
   };
-  assert.equal(selectStdinTransport(firefox152, { jspi: true }), 'buffered');
+  assert.equal(selectStdinTransport(firefox152, { jspi: true }), 'unsupported');
 });
 
 test('e2e: stdin session routing ignores late messages from previous runs', () => {
diff --git a/scripts/e2e-run-request.test.mjs b/scripts/e2e-run-request.test.mjs
index 13a3ba5..fa304bb 100644
--- a/scripts/e2e-run-request.test.mjs
+++ b/scripts/e2e-run-request.test.mjs
@@ -2,7 +2,6 @@ import test from 'node:test';
 import assert from 'node:assert/strict';
 
 import {
-  BUFFERED_STDIN_MAX_BYTES,
   INTERACTIVE_STDIN_CHUNK_MAX_BYTES,
   validateRunRequest,
   validateStdinMessage,
@@ -35,18 +34,6 @@ test('e2e: worker run contract accepts and normalizes all stdin modes', () => {
     sessionId: 'stdin-session-1',
   });
 
-  const buffered = validateRunRequest(interactiveRequest({
-    stdinMode: 'buffered',
-    sharedBuffer: undefined,
-    stdinBuffer: new TextEncoder().encode('Ada\n41\n').buffer,
-  }));
-  assert.equal(buffered.ok, true);
-  assert.equal(buffered.value.stdin.mode, 'buffered');
-  assert.deepEqual(
-    [...buffered.value.stdin.bytes],
-    [...new TextEncoder().encode('Ada\n41\n')]
-  );
-
   const none = validateRunRequest(interactiveRequest({
     stdinMode: 'none',
     sharedBuffer: undefined,
@@ -118,15 +105,15 @@ test('e2e: worker stdin message contract rejects malformed and oversized input',
   }
 });
 
-test('e2e: worker run contract rejects buffered stdin above the shared size limit', () => {
+test('e2e: worker run contract rejects buffered stdin entirely', () => {
   const result = validateRunRequest(interactiveRequest({
     stdinMode: 'buffered',
     sharedBuffer: undefined,
-    stdinBuffer: new Uint8Array(BUFFERED_STDIN_MAX_BYTES + 1),
+    stdinBuffer: new Uint8Array([1]),
   }));
 
   assert.equal(result.ok, false);
-  assert.match(result.error, /256 KiB/);
+  assert.match(result.error, /stdin/i);
 });
 
 test('e2e: worker run contract rejects invalid binary and VFS byte fields', () => {
diff --git a/scripts/e2e-terminal-stop.test.mjs b/scripts/e2e-terminal-stop.test.mjs
index 8f0ba21..bcf5fe2 100644
--- a/scripts/e2e-terminal-stop.test.mjs
+++ b/scripts/e2e-terminal-stop.test.mjs
@@ -17,7 +17,6 @@ import {
 function setupTerminalHarness({
   supportsInteractiveStdin = true,
   supportsMessageInteractiveStdin = false,
-  requestBufferedStdin = async () => '',
   onRun,
 } = {}) {
   const writes = [];
@@ -40,7 +39,6 @@ function setupTerminalHarness({
     onRunPreparationStateChange: (preparing) => runPreparationChanges.push(preparing),
     supportsInteractiveStdin: () => supportsInteractiveStdin,
     supportsMessageInteractiveStdin: () => supportsMessageInteractiveStdin,
-    requestBufferedStdin,
     onStdinData: (message) => stdinMessages.push(message),
     onStdinEOF: (message) => stdinMessages.push(message),
     createStdinSessionId: () => 'stdin-session-test',
@@ -152,37 +150,23 @@ test('e2e: normal run completion reports not-running state', async () => {
   assert.equal(__getTerminalStateForTesting().running, false);
 });
 
-test('e2e: non-SAB run posts UTF-8 buffered stdin before entering running state', async () => {
+test('e2e: run without a live stdin transport reports unsupported and posts no request', async () => {
   const ctx = setupTerminalHarness({
     supportsInteractiveStdin: false,
-    requestBufferedStdin: async () => 'Grüße\n',
   });
 
-  assert.equal(await startRun(), true);
-
-  assert.equal(ctx.runCalls.length, 1);
-  assert.equal(ctx.runCalls[0].stdinMode, 'buffered');
-  assert.deepEqual(
-    [...ctx.runCalls[0].stdinBuffer],
-    [...new TextEncoder().encode('Grüße\n')]
-  );
+  assert.equal(await startRun(), false);
+  assert.deepEqual(ctx.runCalls, []);
   assert.deepEqual(ctx.runStateChanges, []);
-  assert.deepEqual(ctx.runPreparationChanges, [true]);
-  assert.equal(__getTerminalStateForTesting().preparingRun, true);
-
-  onRunStart({ stdinMode: 'buffered' });
-  assert.deepEqual(ctx.runStateChanges, [true]);
   assert.deepEqual(ctx.runPreparationChanges, [true, false]);
   assert.equal(__getTerminalStateForTesting().preparingRun, false);
+  assert.ok(ctx.writes.join('').includes('Live terminal stdin is unavailable'));
 });
 
 test('e2e: Firefox JSPI run forwards live terminal lines and EOF by session', async () => {
   const ctx = setupTerminalHarness({
     supportsInteractiveStdin: false,
     supportsMessageInteractiveStdin: true,
-    requestBufferedStdin: async () => {
-      throw new Error('buffered input should not be requested');
-    },
   });
 
   assert.equal(await startRun(), true);
@@ -220,37 +204,6 @@ test('e2e: Firefox JSPI run forwards live terminal lines and EOF by session', as
   });
 });
 
-test('e2e: canceling buffered stdin restores idle state and posts no run request', async () => {
-  const ctx = setupTerminalHarness({
-    supportsInteractiveStdin: false,
-    requestBufferedStdin: async () => null,
-  });
-
-  assert.equal(await startRun(), false);
-
-  assert.deepEqual(ctx.runCalls, []);
-  assert.deepEqual(ctx.runPreparationChanges, [true, false]);
-  assert.equal(__getTerminalStateForTesting().preparingRun, false);
-  assert.equal(__getTerminalStateForTesting().running, false);
-});
-
-test('e2e: duplicate run while buffered input is pending posts only one request', async () => {
-  let resolveInput;
-  const pendingInput = new Promise((resolve) => { resolveInput = resolve; });
-  const ctx = setupTerminalHarness({
-    supportsInteractiveStdin: false,
-    requestBufferedStdin: () => pendingInput,
-  });
-
-  const firstRun = startRun();
-  assert.equal(await startRun(), false);
-  resolveInput('Ada\n');
-  assert.equal(await firstRun, true);
-
-  assert.equal(ctx.runCalls.length, 1);
-  assert.equal(ctx.runCalls[0].stdinMode, 'buffered');
-});
-
 test('e2e: run callback failure restores idle state without run-start', async () => {
   const writes = [];
   __setTerminalTestHarness({
@@ -267,17 +220,3 @@ test('e2e: run callback failure restores idle state without run-start', async ()
   assert.equal(state.running, false);
   assert.ok(writes.join('').includes('Could not start program'));
 });
-
-test('e2e: oversized buffered stdin restores idle state and posts no run request', async () => {
-  const ctx = setupTerminalHarness({
-    supportsInteractiveStdin: false,
-    requestBufferedStdin: async () => 'x'.repeat((256 * 1024) + 1),
-  });
-
-  assert.equal(await startRun(), false);
-
-  assert.deepEqual(ctx.runCalls, []);
-  assert.deepEqual(ctx.runPreparationChanges, [true, false]);
-  assert.equal(__getTerminalStateForTesting().preparingRun, false);
-  assert.ok(ctx.writes.join('').includes('256 KiB'));
-});
diff --git a/scripts/e2e-wasi-shim.test.mjs b/scripts/e2e-wasi-shim.test.mjs
index 730b713..0cc1868 100644
--- a/scripts/e2e-wasi-shim.test.mjs
+++ b/scripts/e2e-wasi-shim.test.mjs
@@ -51,53 +51,11 @@ function writeString(memory, ptr, text) {
   return bytes.length;
 }
 
-test('e2e: wasi shim drains buffered stdin across iovecs and repeated reads', () => {
-  const input = new TextEncoder().encode('Ada\n41');
-  const { runtime } = makeRuntime({ mode: 'buffered', bytes: input });
-
-  const first = readStdin(runtime, [
-    { base: 128, len: 2 },
-    { base: 160, len: 3 },
-  ]);
-  assert.equal(first.errno, 0);
-  assert.equal(first.nread, 5);
-  assert.equal(new TextDecoder().decode(first.bytes.subarray(128, 130)), 'Ad');
-  assert.equal(new TextDecoder().decode(first.bytes.subarray(160, 163)), 'a\n4');
-
-  const second = readStdin(runtime, [{ base: 192, len: 8 }]);
-  assert.equal(second.errno, 0);
-  assert.equal(second.nread, 1);
-  assert.equal(new TextDecoder().decode(second.bytes.subarray(192, 193)), '1');
-
-  const eof = readStdin(runtime, [{ base: 224, len: 8 }]);
-  assert.equal(eof.errno, 0);
-  assert.equal(eof.nread, 0);
-});
-
-test('e2e: wasi shim preserves UTF-8 bytes and input without a trailing newline', () => {
-  const input = new TextEncoder().encode('Grüße');
-  const { runtime } = makeRuntime({ mode: 'buffered', bytes: input });
-
-  const result = readStdin(runtime, [{ base: 128, len: 32 }]);
-
+test('e2e: wasi shim returns immediate EOF for none stdin', () => {
+  const { runtime } = makeRuntime({ mode: 'none' });
+  const result = readStdin(runtime, [{ base: 128, len: 8 }]);
   assert.equal(result.errno, 0);
-  assert.equal(result.nread, input.length);
-  assert.deepEqual(
-    [...result.bytes.subarray(128, 128 + result.nread)],
-    [...input]
-  );
-});
-
-test('e2e: wasi shim returns immediate EOF for empty buffered and none stdin', () => {
-  for (const stdin of [
-    { mode: 'buffered', bytes: new Uint8Array() },
-    { mode: 'none' },
-  ]) {
-    const { runtime } = makeRuntime(stdin);
-    const result = readStdin(runtime, [{ base: 128, len: 8 }]);
-    assert.equal(result.errno, 0);
-    assert.equal(result.nread, 0);
-  }
+  assert.equal(result.nread, 0);
 });
 
 test('e2e: wasi shim suspends message stdin until data arrives', async () => {
@@ -139,22 +97,6 @@ test('e2e: wasi shim returns immediately for a zero-length message stdin read',
   assert.equal(result.nread, 0);
 });
 
-test('e2e: wasi shim drains long buffered input without truncation', () => {
-  const input = new Uint8Array(32 * 1024);
-  input.forEach((_, index) => { input[index] = index % 251; });
-  const { runtime } = makeRuntime({ mode: 'buffered', bytes: input });
-  const memory = { buffer: new ArrayBuffer(64 * 1024) };
-  runtime.setMemory(memory);
-
-  const result = readStdin(runtime, [{ base: 1024, len: input.length }]);
-
-  assert.equal(result.nread, input.length);
-  assert.deepEqual(
-    result.bytes.subarray(1024, 1024 + input.length),
-    input
-  );
-});
-
 test('e2e: wasi shim exposes callable fd_fdstat_set_flags', () => {
   const { runtime } = makeRuntime();
   assert.equal(typeof runtime.wasi.fd_fdstat_set_flags, 'function');
diff --git a/src/ui/browser-capabilities.mjs b/src/ui/browser-capabilities.mjs
index e874bdd..255e9cc 100644
--- a/src/ui/browser-capabilities.mjs
+++ b/src/ui/browser-capabilities.mjs
@@ -126,7 +126,7 @@ export function collectBrowserCapabilities(root = globalThis, workerCapabilities
       ? 'interactive'
       : jspiInteractiveStdin
         ? 'interactive-message'
-        : 'buffered',
+      : 'unsupported',
   };
 }
 
@@ -144,7 +144,7 @@ export function selectStdinTransport(capabilities, workerCapabilities = {}) {
   ) {
     return 'message-jspi';
   }
-  return 'buffered';
+  return 'unsupported';
 }
 
 export function createBrowserCompatibilityReport(root = globalThis, workerCapabilities = {}) {
@@ -194,7 +194,7 @@ export function createBrowserCompatibilityReport(root = globalThis, workerCapabi
     if (!capabilities.interactiveStdin) {
       limitations.push({
         key: 'limitedInteractiveStdin',
-        label: 'Firefox uses pre-supplied buffered stdin; live interactive terminal input is unavailable.',
+        label: 'Firefox requires worker-side JSPI for live terminal stdin.',
       });
     }
     limitations.push({
diff --git a/src/ui/buffered-stdin-dialog.mjs b/src/ui/buffered-stdin-dialog.mjs
deleted file mode 100644
index 2c88904..0000000
--- a/src/ui/buffered-stdin-dialog.mjs
+++ /dev/null
@@ -1,78 +0,0 @@
-'use strict';
-
-import { BUFFERED_STDIN_MAX_BYTES } from '../workers/run-request.mjs';
-
-export function requestBufferedStdin() {
-  const dialog = document.getElementById('buffered-stdin-dialog');
-  const input = document.getElementById('buffered-stdin-input');
-  const feedback = document.getElementById('buffered-stdin-feedback');
-  const runButton = document.getElementById('buffered-stdin-run');
-  const cancelButton = document.getElementById('buffered-stdin-cancel');
-
-  if (!dialog || !input || !feedback || !runButton || !cancelButton) {
-    throw new Error('Buffered stdin dialog is unavailable.');
-  }
-
-  const previouslyFocused = document.activeElement;
-  input.value = '';
-  input.removeAttribute('aria-invalid');
-  feedback.classList.remove('is-error');
-
-  return new Promise((resolve) => {
-    let settled = false;
-
-    const updateFeedback = () => {
-      const byteLength = new TextEncoder().encode(input.value).byteLength;
-      feedback.textContent =
-        `${byteLength.toLocaleString()} / ${BUFFERED_STDIN_MAX_BYTES.toLocaleString()} bytes`;
-      feedback.classList.remove('is-error');
-      input.removeAttribute('aria-invalid');
-      return byteLength;
-    };
-
-    const cleanup = () => {
-      input.removeEventListener('input', updateFeedback);
-      runButton.removeEventListener('click', submit);
-      cancelButton.removeEventListener('click', cancel);
-      dialog.removeEventListener('cancel', cancel);
-      dialog.removeEventListener('close', cancel);
-    };
-
-    const finish = (value) => {
-      if (settled) return;
-      settled = true;
-      cleanup();
-      if (dialog.open) dialog.close();
-      previouslyFocused?.focus?.();
-      resolve(value);
-    };
-
-    const submit = () => {
-      const byteLength = updateFeedback();
-      if (byteLength > BUFFERED_STDIN_MAX_BYTES) {
-        feedback.textContent =
-          `Input is too large. Keep pre-supplied stdin at or below ${BUFFERED_STDIN_MAX_BYTES.toLocaleString()} bytes.`;
-        feedback.classList.add('is-error');
-        input.setAttribute('aria-invalid', 'true');
-        input.focus();
-        return;
-      }
-      finish(input.value);
-    };
-
-    const cancel = (event) => {
-      event?.preventDefault?.();
-      finish(null);
-    };
-
-    input.addEventListener('input', updateFeedback);
-    runButton.addEventListener('click', submit);
-    cancelButton.addEventListener('click', cancel);
-    dialog.addEventListener('cancel', cancel);
-    dialog.addEventListener('close', cancel);
-
-    updateFeedback();
-    dialog.showModal();
-    input.focus();
-  });
-}
diff --git a/src/ui/index.html b/src/ui/index.html
index eca57cf..5046354 100644
--- a/src/ui/index.html
+++ b/src/ui/index.html
@@ -97,29 +97,6 @@
 
   </div>
 
-  <dialog id="buffered-stdin-dialog" aria-labelledby="buffered-stdin-title">
-    <div class="buffered-stdin-content">
-      <h2 id="buffered-stdin-title">Pre-supplied stdin</h2>
-      <p>
-        Live interactive input is unavailable in this browser. Enter all input
-        before the program starts; it will receive EOF after these bytes.
-      </p>
-      <label for="buffered-stdin-input">Program input</label>
-      <textarea
-        id="buffered-stdin-input"
-        rows="8"
-        maxlength="262144"
-        spellcheck="false"
-        aria-describedby="buffered-stdin-feedback"
-      ></textarea>
-      <div id="buffered-stdin-feedback" aria-live="polite">0 / 262,144 bytes</div>
-      <div class="buffered-stdin-actions">
-        <button type="button" id="buffered-stdin-cancel">Cancel</button>
-        <button type="button" id="buffered-stdin-run" class="btn-primary">Run program</button>
-      </div>
-    </div>
-  </dialog>
-
   <!-- bundle.js injected by HtmlWebpackPlugin -->
 </body>
 </html>
diff --git a/src/ui/styles.css b/src/ui/styles.css
index e7d176a..972d423 100644
--- a/src/ui/styles.css
+++ b/src/ui/styles.css
@@ -561,76 +561,3 @@ body.is-resizing-horizontal * {
 .session-reload-actions .session-reload-primary:hover {
   filter: brightness(1.05);
 }
-
-/* ── Buffered stdin prompt ────────────────────────────────────────────────── */
-
-#buffered-stdin-dialog {
-  width: min(520px, calc(100vw - 32px));
-  max-height: calc(100vh - 32px);
-  margin: auto;
-  padding: 0;
-  overflow: auto;
-  color: var(--text);
-  background: var(--mantle);
-  border: 1px solid var(--surface1);
-  border-radius: 8px;
-  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.45);
-}
-
-#buffered-stdin-dialog::backdrop {
-  background: rgba(17, 17, 27, 0.72);
-}
-
-.buffered-stdin-content {
-  display: flex;
-  flex-direction: column;
-  gap: 10px;
-  padding: 20px;
-}
-
-.buffered-stdin-content h2 {
-  font-size: 15px;
-}
-
-.buffered-stdin-content p,
-#buffered-stdin-feedback {
-  color: var(--subtext0);
-  line-height: 1.45;
-}
-
-.buffered-stdin-content label {
-  font-weight: 600;
-}
-
-#buffered-stdin-input {
-  width: 100%;
-  min-height: 120px;
-  resize: vertical;
-  padding: 8px;
-  color: var(--text);
-  background: var(--crust);
-  border: 1px solid var(--surface1);
-  border-radius: 4px;
-  font: 13px/1.4 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;
-}
-
-#buffered-stdin-input:focus {
-  border-color: var(--blue);
-  outline: 1px solid var(--blue);
-}
-
-#buffered-stdin-feedback {
-  min-height: 18px;
-  font-size: 12px;
-  text-align: right;
-}
-
-#buffered-stdin-feedback.is-error {
-  color: var(--red);
-}
-
-.buffered-stdin-actions {
-  display: flex;
-  justify-content: flex-end;
-  gap: 8px;
-}
diff --git a/src/ui/terminal.js b/src/ui/terminal.js
index a97b337..22fe43a 100644
--- a/src/ui/terminal.js
+++ b/src/ui/terminal.js
@@ -31,11 +31,7 @@ import {
   normalizeOverlayPath,
 } from './build-request.mjs';
 import { validateNewDirectoryPath, validateNewFilePath } from './workspace-fs.mjs';
-import {
-  BUFFERED_STDIN_MAX_BYTES,
-  INTERACTIVE_STDIN_CHUNK_MAX_BYTES,
-} from '../workers/run-request.mjs';
-import { requestBufferedStdin } from './buffered-stdin-dialog.mjs';
+import { INTERACTIVE_STDIN_CHUNK_MAX_BYTES } from '../workers/run-request.mjs';
 import {
   collectBrowserCapabilities,
   selectStdinTransport,
@@ -231,7 +227,6 @@ let _supportsInteractiveStdin = supportsInteractiveStdin;
 let _workerCapabilities = { jspi: false };
 let _getStdinTransport = getStdinTransport;
 let _createStdinSessionId = createStdinSessionId;
-let _requestBufferedStdin = requestBufferedStdin;
 
 function supportsInteractiveStdin() {
   return (
@@ -264,7 +259,7 @@ function createStdinSessionId() {
  * @param {HTMLElement} container
  * @param {{
  *   onCompile: (request:{sourcePaths:(string[]|null), flags:string[], std:string, outputName:(string|null), cwd:string}) => void,
- *   onRun:     (request:{stdinMode:string,sharedBuffer?:SharedArrayBuffer,stdinBuffer?:Uint8Array}) => Promise<void>|void,
+ *   onRun:     (request:{stdinMode:string,sharedBuffer?:SharedArrayBuffer,stdinSessionId?:string}) => Promise<void>|void,
  *   onStopRun?: () => void,
  *   onStdinData?: (message:{type:'stdin-data',stdinSessionId:string,bytes:Uint8Array}) => void,
  *   onStdinEOF?: (message:{type:'stdin-eof',stdinSessionId:string}) => void,
@@ -303,7 +298,6 @@ export function createTerminal(container, {
   _supportsInteractiveStdin = supportsInteractiveStdin;
   _getStdinTransport = getStdinTransport;
   _createStdinSessionId = createStdinSessionId;
-  _requestBufferedStdin = requestBufferedStdin;
   initialPromptShown = false;
   busy = true;
 
@@ -385,8 +379,8 @@ export function setWorkerCapabilities(capabilities = {}) {
  * Start executing the last compiled binary.
  *
  * Uses live SharedArrayBuffer stdin when cross-origin isolation is available,
- * Firefox JSPI message stdin when its worker confirms support, and otherwise
- * collects pre-supplied buffered stdin before dispatch.
+ * Firefox JSPI message stdin when its worker confirms support. Unsupported
+ * runtimes are rejected before a worker run request is posted.
  * Can be called from the terminal command line (`./a.out`) or directly from
  * the toolbar Run button.
  *
@@ -419,19 +413,9 @@ export async function startRun() {
         stdinSessionId: activeStdinSessionId,
       };
     } else {
-      const text = await _requestBufferedStdin();
-      if (text === null) {
-        setRunPreparationState(false);
-        busy = false;
-        writePrompt();
-        return false;
-      }
-
-      const stdinBuffer = new TextEncoder().encode(text);
-      if (stdinBuffer.byteLength > BUFFERED_STDIN_MAX_BYTES) {
-        throw new Error('Buffered stdin exceeds the 256 KiB limit.');
-      }
-      request = { stdinMode: 'buffered', stdinBuffer };
+      throw new Error(
+        'Live terminal stdin is unavailable in this browser/runtime. Firefox requires JSPI support; Chromium requires SharedArrayBuffer support.'
+      );
     }
 
     if (!_onRun) throw new Error('Run callback is unavailable.');
@@ -1101,7 +1085,6 @@ export function __setTerminalTestHarness({
   supportsInteractiveStdin: supportsInteractiveStdinForTest = () => true,
   supportsMessageInteractiveStdin: supportsMessageInteractiveStdinForTest = () => false,
   createStdinSessionId: createStdinSessionIdForTest = () => 'stdin-session-test',
-  requestBufferedStdin: requestBufferedStdinForTest = async () => '',
 } = {}) {
   term = terminalInstance || null;
   fitAddon = null;
@@ -1120,10 +1103,9 @@ export function __setTerminalTestHarness({
   _getStdinTransport = () => {
     if (supportsInteractiveStdinForTest()) return 'shared-buffer';
     if (supportsMessageInteractiveStdinForTest()) return 'message-jspi';
-    return 'buffered';
+    return 'unsupported';
   };
   _createStdinSessionId = createStdinSessionIdForTest;
-  _requestBufferedStdin = requestBufferedStdinForTest;
   lastBuiltArtifactPath = artifactPath;
   inputBuffer = '';
   history.length = 0;
diff --git a/src/workers/compiler.worker.js b/src/workers/compiler.worker.js
index 2ac8df4..fb6f4cc 100644
--- a/src/workers/compiler.worker.js
+++ b/src/workers/compiler.worker.js
@@ -14,8 +14,6 @@
  *                   vfsFiles, binaryBytes?: Uint8Array }
  *    { type: 'stdin-data', stdinSessionId: string, bytes: Uint8Array }
  *    { type: 'stdin-eof', stdinSessionId: string }
- *    { type: 'run', stdinMode: 'buffered', stdinBuffer: Uint8Array|ArrayBuffer,
- *                   vfsFiles, binaryBytes?: Uint8Array }
  *    { type: 'run', stdinMode: 'none', vfsFiles, binaryBytes?: Uint8Array }
  *    { type: 'status'  }
  *
@@ -493,7 +491,6 @@ function groupDiagnostics(text) {
  * @param {{
  *   stdin: ({mode:'interactive',sharedBuffer:SharedArrayBuffer}|
  *           {mode:'interactive-message',sessionId:string}|
- *           {mode:'buffered',bytes:Uint8Array}|
  *           {mode:'none'}),
  *   vfsFiles:Array<{path:string,bytes:Uint8Array}>,
  *   binaryBytes:Uint8Array|null
diff --git a/src/workers/run-request.mjs b/src/workers/run-request.mjs
index ddd3bf2..aef1921 100644
--- a/src/workers/run-request.mjs
+++ b/src/workers/run-request.mjs
@@ -1,6 +1,5 @@
 'use strict';
 
-export const BUFFERED_STDIN_MAX_BYTES = 256 * 1024;
 export const INTERACTIVE_STDIN_CHUNK_MAX_BYTES = 64 * 1024;
 const STDIN_SESSION_ID_MAX_LENGTH = 128;
 
@@ -103,16 +102,6 @@ export function validateRunRequest(request) {
       };
       break;
 
-    case 'buffered':
-      if (!isByteSource(request.stdinBuffer) || request.sharedBuffer !== undefined) {
-        return invalid('Invalid buffered stdin: stdinBuffer must be a Uint8Array or ArrayBuffer.');
-      }
-      if (request.stdinBuffer.byteLength > BUFFERED_STDIN_MAX_BYTES) {
-        return invalid('Invalid buffered stdin: input exceeds the 256 KiB limit.');
-      }
-      stdin = { mode: 'buffered', bytes: asUint8Array(request.stdinBuffer) };
-      break;
-
     case 'none':
       if (request.sharedBuffer !== undefined || request.stdinBuffer !== undefined) {
         return invalid('Invalid none stdin: no stdin buffer may be supplied.');
@@ -122,7 +111,7 @@ export function validateRunRequest(request) {
 
     default:
       return invalid(
-        'Invalid stdinMode. Expected interactive, interactive-message, buffered, or none.'
+        'Invalid stdinMode. Expected interactive, interactive-message, or none.'
       );
   }
 
diff --git a/src/workers/wasi-shim.mjs b/src/workers/wasi-shim.mjs
index f0464b7..df40dd4 100644
--- a/src/workers/wasi-shim.mjs
+++ b/src/workers/wasi-shim.mjs
@@ -55,8 +55,6 @@ export function createWasiRuntime({
   const messageStdinChunks = [];
   let messageStdinChunkIndex = 0;
   let messageStdinChunkOffset = 0;
-  let stdinBytes = new Uint8Array();
-  let stdinCursor = 0;
   let stdinEnded = false;
   const stdinWaiters = [];
 
@@ -69,11 +67,6 @@ export function createWasiRuntime({
     }
     sharedBuffer = stdin.sharedBuffer;
     sabControl = new Int32Array(sharedBuffer);
-  } else if (stdinMode === 'buffered') {
-    if (!(stdin.bytes instanceof Uint8Array) && !(stdin.bytes instanceof ArrayBuffer)) {
-      throw new TypeError('Buffered stdin requires Uint8Array or ArrayBuffer bytes.');
-    }
-    stdinBytes = new Uint8Array(stdin.bytes);
   } else if (stdinMode !== 'none' && stdinMode !== 'interactive-message') {
     throw new TypeError(`Unsupported stdin mode: ${String(stdinMode)}`);
   }
@@ -289,19 +282,6 @@ export function createWasiRuntime({
         return WASI_ERRNO_SUCCESS;
       }
 
-      if (stdinMode === 'buffered') {
-        for (const { base, len } of spans) {
-          const available = stdinBytes.length - stdinCursor;
-          if (available <= 0) break;
-          const toRead = Math.min(len, available);
-          u8().set(stdinBytes.subarray(stdinCursor, stdinCursor + toRead), base);
-          stdinCursor += toRead;
-          total += toRead;
-        }
-        view().setUint32(nreadPtr, total, true);
-        return WASI_ERRNO_SUCCESS;
-      }
-
       for (const { base, len } of spans) {
         if (stdinQueue.length === 0) {
           if (Atomics.load(sabControl, 0) === 0) {