diff --git a/.github/workflows/build-whisper-stt.yml b/.github/workflows/build-whisper-stt.yml
index f5a4dd2f..e63eba23 100644
--- a/.github/workflows/build-whisper-stt.yml
+++ b/.github/workflows/build-whisper-stt.yml
@@ -54,7 +54,16 @@ jobs:
             tag: darwin-x64
             label: macOS x64 (CPU)
             vulkan: false
-          - os: ubuntu-latest
+          # PINNED, and not `ubuntu-latest` — see the long comment on build.yml's
+          # build-linux job. This leg produces the WORST offender of the two: built on
+          # 24.04, whisper-stt-server and the libggml backends needed GLIBC_2.38 and
+          # GLIBCXX_3.4.32, so they died in ld.so on Ubuntu 22.04, Debian 12 and RHEL 9
+          # and transcription failed there with an unactionable developer error. The
+          # symbols were never asked for: `__isoc23_strtol` is glibc 2.38's C23 redirect
+          # and `_ZSt21ios_base_library_initv` is emitted into every TU that includes
+          # <iostream> by GCC 13.2+. 22.04 has the CMake (3.22 >= the 3.20 required) and
+          # a C++20 compiler; nothing here uses a GCC 13-only library feature.
+          - os: ubuntu-22.04
             arch: x64
             tag: linux-x64
             label: Linux x64 (Vulkan + CPU fallback)
@@ -73,7 +82,10 @@ jobs:
         uses: ./.github/actions/setup
 
       - name: Install Ninja (Linux)
-        if: matrix.os == 'ubuntu-latest'
+        # `startsWith`, matching the macOS step below, rather than an exact image name:
+        # this was `== 'ubuntu-latest'`, so pinning the image would have skipped Ninja
+        # silently instead of failing.
+        if: startsWith(matrix.os, 'ubuntu')
         run: |
           sudo apt-get update
           sudo apt-get install -y ninja-build build-essential
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 8ce503db..59ee3a15 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -490,7 +490,25 @@ jobs:
 
   build-linux:
     name: Linux packages
-    runs-on: ubuntu-latest
+    # PINNED, and not to `ubuntu-latest`. The linker binds every symbol to the newest
+    # version its BUILD machine offers, so the runner image silently decides the oldest
+    # distro these packages can run on — nothing in the source asks for any of it.
+    # On ubuntu-latest (24.04) that floor was glibc 2.38 / GLIBCXX_3.4.32, which put
+    # Ubuntu 22.04, Debian 12 and RHEL 9 out of range: whisper-stt-server and the ggml
+    # backends died in ld.so before main(), and compositor_view.node (2.35, from a single
+    # `hypotf`) died on RHEL 9 as well. Both fail SILENTLY — the app still launches,
+    # captions just report a developer error and the preview renders nothing — and no
+    # package format catches it, because the deb/rpm/pacman `depends` lists are
+    # hand-written in electron-builder.json5 and electron-builder passes fpm none of
+    # --rpm-autoreq*, so not even dnf generates the libc.so.6(GLIBC_2.38) requirement
+    # that would have refused the install.
+    #
+    # 22.04 is the oldest distro the README claims (it names it as the PipeWire
+    # baseline), and it is the binding one: glibc 2.35 and libstdc++6 from GCC 12
+    # (GLIBCXX_3.4.30, CXXABI_1.3.13), against Debian 12's 2.36/3.4.30/1.3.13.
+    # scripts/before-pack.cjs enforces that ceiling on the built payload, so bumping
+    # this image alone cannot quietly raise the floor again.
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout code
         uses: actions/checkout@v7
@@ -501,13 +519,28 @@ jobs:
       # bsdtar (libarchive-tools) is fpm's mtree generator for the pacman target.
       # rpmbuild (rpm) is what fpm shells out to for the rpm target; without it the
       # build fails at packaging, not at config parse.
+      - name: Install Linux packaging dependencies
+        run: sudo apt-get update && sudo apt-get install -y libarchive-tools rpm
+
       # patchelf is what build-linux-compositor-addon.mjs renames the ffmpeg symbols
       # with, so the addon cannot bind to Chromium's bundled ffmpeg — an unconditional
-      # dependency that resolvePatchelf() throws on. It happens to be preinstalled on
-      # the ubuntu-24.04 image, which is why this has worked; declaring it means the
-      # build stops depending on the runner image's contents.
-      - name: Install Linux packaging and native build dependencies
-        run: sudo apt-get update && sudo apt-get install -y libarchive-tools rpm patchelf
+      # dependency that resolvePatchelf() throws on.
+      #
+      # NOT from apt, which is the whole reason this is its own step: 22.04 carries
+      # patchelf 0.14.3 and `--rename-dynamic-symbols` first shipped in 0.18.0, so the
+      # apt copy fails the rename outright. 0.18.0 is also exactly what the 24.04 image
+      # provided, so the renaming behaviour is unchanged from what already ships.
+      # resolvePatchelf() checks ~/.local/bin before /usr/bin, so this wins over
+      # whatever the image happens to carry.
+      - name: Install patchelf
+        run: |
+          curl -fsSLo /tmp/patchelf.tar.gz \
+            https://github.com/NixOS/patchelf/releases/download/0.18.0/patchelf-0.18.0-x86_64.tar.gz
+          echo "ce84f2447fb7a8679e58bc54a20dc2b01b37b5802e12c57eece772a6f14bf3f0  /tmp/patchelf.tar.gz" | sha256sum -c -
+          mkdir -p ~/.local/bin
+          tar -xzf /tmp/patchelf.tar.gz -C /tmp ./bin/patchelf
+          mv /tmp/bin/patchelf ~/.local/bin/patchelf
+          ~/.local/bin/patchelf --version
 
       - name: Stage whisper-stt binaries
         shell: bash
diff --git a/scripts/before-pack.cjs b/scripts/before-pack.cjs
index 83752c1f..26421796 100644
--- a/scripts/before-pack.cjs
+++ b/scripts/before-pack.cjs
@@ -299,6 +299,188 @@ function checkLinuxNativePayload(context) {
 				"renamed to `osff_*` for the compositor addon, and the helper needs the originals.",
 		);
 	}
+
+	checkLinuxSymbolVersionFloor(dir);
+}
+
+/**
+ * The highest versioned symbol a shipped ELF may require, per version prefix.
+ *
+ * The Linux counterpart of the Windows import-table guard (checkWinNoRedistDependency
+ * and importedDlls(), from #321 — this may land first, in which case they arrive with
+ * it), and the same failure that hook could not see: the linker binds each symbol to
+ * the newest version the BUILD machine
+ * offers, so the runner image silently decides the oldest distro the packages run on.
+ * It works on every developer machine and in CI by construction, and only the target
+ * distro tells the truth.
+ *
+ * Nothing in the source asks for any of it. Built on ubuntu-latest (24.04) the payload
+ * needed GLIBC_2.38 for four `__isoc23_strto*` — glibc 2.38's C23 redirect of `strtol`
+ * — GLIBCXX_3.4.32 for `_ZSt21ios_base_library_initv`, which GCC 13.2+ emits into every
+ * translation unit that includes <iostream>, and GLIBC_2.35 for one `hypotf`, a symbol
+ * that has existed since 2.2.5 and whose newest version Rust's f32::hypot simply took.
+ *
+ * That shipped: on Ubuntu 22.04, Debian 12 and RHEL 9, whisper-stt-server and the ggml
+ * backends died in ld.so before main() (transcription and captions fail with a developer
+ * error), and on RHEL 9 compositor_view.node failed require() as well (no preview, and
+ * every export falls back to the no-op compositor). The app still LAUNCHES on all of
+ * them — Electron itself only needs 2.25 — so it reads as a broken app rather than a
+ * broken package, and nothing in any log says otherwise. No package format catches it
+ * either: the deb/rpm/pacman `depends` lists are hand-written in electron-builder.json5,
+ * and electron-builder passes fpm none of --rpm-autoreq*, so not even dnf generates the
+ * `libc.so.6(GLIBC_2.38)` requirement that would have refused the install.
+ *
+ * The ceiling is what the OLDEST distro the README claims actually provides. Ubuntu
+ * 22.04 is the binding one — glibc 2.35, libstdc++6 from GCC 12 — against Debian 12's
+ * 2.36 with the same libstdc++. Raising any of these is a decision to drop a distro
+ * from the README, not a build detail; the runners are pinned to match (build.yml's
+ * build-linux and build-whisper-stt.yml).
+ */
+const MAX_SYMBOL_VERSION = { GLIBC: "2.35", GLIBCXX: "3.4.30", CXXABI: "1.3.13" };
+
+/** Dotted numeric compare, so 3.4.9 < 3.4.30 and 2.4 < 2.38 rather than by string. */
+function compareVersions(a, b) {
+	const left = a.split(".").map(Number);
+	const right = b.split(".").map(Number);
+	for (let i = 0; i < Math.max(left.length, right.length); i++) {
+		if ((left[i] ?? 0) !== (right[i] ?? 0)) return (left[i] ?? 0) - (right[i] ?? 0);
+	}
+	return 0;
+}
+
+/**
+ * The highest version an ELF needs per prefix, as `{ GLIBC: "2.38", GLIBCXX: "3.4.32" }`.
+ *
+ * Reads `.gnu.version_r` (the version NEEDS) and deliberately not `.gnu.version_d` (the
+ * version DEFINITIONS): libc and libstdc++ define every version they ever shipped, so
+ * reading definitions would report a bundled library as needing itself. Parsed here
+ * rather than shelled out to readelf for the same reason importedDlls() does not use
+ * dumpbin — binutils is not installed on every machine that packages this.
+ *
+ * 64-bit little-endian only, which is every arch this ships (x86_64, aarch64).
+ */
+function neededSymbolVersions(file) {
+	const b = fs.readFileSync(file);
+	if (b.readUInt32BE(0) !== 0x7f454c46) throw new Error(`${file} is not an ELF binary`);
+	if (b[4] !== 2 || b[5] !== 1) throw new Error(`${file} is not 64-bit little-endian ELF`);
+
+	const shoff = Number(b.readBigUInt64LE(0x28));
+	const shentsize = b.readUInt16LE(0x3a);
+	const SHT_GNU_VERNEED = 0x6ffffffe;
+
+	let section;
+	for (let i = 0; i < b.readUInt16LE(0x3c); i++) {
+		const sh = shoff + i * shentsize;
+		if (b.readUInt32LE(sh + 4) !== SHT_GNU_VERNEED) continue;
+		// sh_info is the Verneed count; sh_link is the string table these names live in.
+		const strtabHeader = shoff + b.readUInt32LE(sh + 0x28) * shentsize;
+		section = {
+			offset: Number(b.readBigUInt64LE(sh + 0x18)),
+			count: b.readUInt32LE(sh + 0x2c),
+			strtab: Number(b.readBigUInt64LE(strtabHeader + 0x18)),
+		};
+		break;
+	}
+	// No such section means the binary needs no versioned symbols at all — legitimate
+	// for a fully static one, and nothing to check either way.
+	if (!section) return {};
+
+	const nameAt = (at) =>
+		b.subarray(section.strtab + at, b.indexOf(0, section.strtab + at)).toString("latin1");
+
+	const highest = {};
+	let verneed = section.offset;
+	for (let i = 0; i < section.count; i++) {
+		let vernaux = verneed + b.readUInt32LE(verneed + 8);
+		for (let j = 0; j < b.readUInt16LE(verneed + 2); j++) {
+			// "GLIBC_2.38" -> prefix GLIBC, version 2.38. Anything not shaped like that
+			// (there is none in practice) is skipped rather than guessed at.
+			const [, prefix, version] =
+				/^(.+)_(\d+(?:\.\d+)*)$/.exec(nameAt(b.readUInt32LE(vernaux + 8))) ?? [];
+			if (prefix && (!highest[prefix] || compareVersions(version, highest[prefix]) > 0)) {
+				highest[prefix] = version;
+			}
+			vernaux += b.readUInt32LE(vernaux + 12);
+		}
+		verneed += b.readUInt32LE(verneed + 12);
+	}
+	return highest;
+}
+
+/** Every ELF under `dir`, recursively — the helper's ffmpeg sits in a subdirectory. */
+function elfFilesUnder(dir) {
+	const found = [];
+	for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+		const full = path.join(dir, entry.name);
+		if (entry.isDirectory()) {
+			found.push(...elfFilesUnder(full));
+			continue;
+		}
+		if (!entry.isFile()) continue;
+		// By magic, not by extension: the helpers, whisper-stt-server and ffmpeg have none.
+		const magic = Buffer.alloc(4);
+		const fd = fs.openSync(full, "r");
+		try {
+			fs.readSync(fd, magic, 0, 4, 0);
+		} finally {
+			fs.closeSync(fd);
+		}
+		if (magic.readUInt32BE(0) === 0x7f454c46) found.push(full);
+	}
+	return found;
+}
+
+/** Nothing we ship may need a newer glibc or libstdc++ than MAX_SYMBOL_VERSION allows. */
+function checkLinuxSymbolVersionFloor(dir) {
+	const scanned = elfFilesUnder(dir).map((file) => ({
+		name: path.relative(dir, file),
+		needs: neededSymbolVersions(file),
+	}));
+
+	// The same assertion checkWinNoRedistDependency makes, for the same reason: a guard
+	// that silently stops looking reports "clean" for the rest of the project's life.
+	// Every dynamically linked binary in this payload needs versioned glibc symbols, so
+	// finding none anywhere means the parser broke. Asserted across the scan rather than
+	// per file, because a genuinely static binary legitimately has no .gnu.version_r.
+	if (!scanned.some((entry) => entry.needs.GLIBC)) {
+		throw new Error(
+			`Refusing to package: read no glibc symbol versions from any of the ${scanned.length} ` +
+				`ELF files in ${path.relative(ROOT, dir)}.\n\n` +
+				"Every one of them links glibc, so this is a bug in neededSymbolVersions()\n" +
+				"(scripts/before-pack.cjs), not a self-contained payload. Fix the parser — leaving\n" +
+				"it is how packages that cannot start on the supported distros get shipped again.",
+		);
+	}
+
+	const offenders = scanned
+		.map((entry) => ({
+			name: entry.name,
+			bad: Object.entries(MAX_SYMBOL_VERSION)
+				.filter(
+					([prefix, max]) => entry.needs[prefix] && compareVersions(entry.needs[prefix], max) > 0,
+				)
+				.map(([prefix, max]) => `${prefix}_${entry.needs[prefix]} (max ${prefix}_${max})`),
+		}))
+		.filter((entry) => entry.bad.length > 0);
+	if (offenders.length === 0) {
+		return;
+	}
+
+	throw new Error(
+		"Refusing to package binaries that need a newer glibc or libstdc++ than the oldest\n" +
+			"supported distro provides.\n\n" +
+			`  looked in: ${path.relative(ROOT, dir)}\n\n` +
+			`${offenders.map((o) => `  - ${o.name} needs ${o.bad.join(", ")}`).join("\n")}\n\n` +
+			"Almost certainly nothing asked for this: the linker binds each symbol to the newest\n" +
+			"version the build machine offers, so this means something was built on a newer image\n" +
+			"than the floor. On the target it dies in ld.so before main() or fails require(), while\n" +
+			"the app still launches — so it reads as a broken app, and no package format catches it.\n\n" +
+			"Build on the pinned runners: ubuntu-22.04 in .github/workflows/build.yml (build-linux)\n" +
+			"and build-whisper-stt.yml. To see which symbols pulled a version in:\n\n" +
+			"    readelf -V <file>\n" +
+			"    readelf -W --dyn-syms <file> | grep @GLIBC_2.38\n\n" +
+			"Raising MAX_SYMBOL_VERSION drops a distro the README claims to support.",
+	);
 }
 
 /** Newest mtime under `target` (file or directory), or 0 if it does not exist. */