diff --git a/docs/process-capture.md b/docs/process-capture.md
index 6673cd1fc0..57df119a9d 100644
--- a/docs/process-capture.md
+++ b/docs/process-capture.md
@@ -257,7 +257,9 @@ A bare executable name uses the scenario's `PATH` override, then the inherited
 An explicitly empty `PATH` searches only the working directory. Executable,
 working-directory, and observation paths preserve native `symlink/..` traversal.
 
-Terminal dimensions must satisfy `columns × (rows + scrollback) ≤ 1,000,000`.
+Terminal width must be at least two columns: the pinned xterm renderer cannot
+represent a one-column screen. This applies to the initial size and every resize.
+Terminal dimensions must also satisfy `columns × (rows + scrollback) ≤ 1,000,000`.
 Every scheduled resize uses the same selected scrollback and must fit this
 working-buffer budget. REA rejects oversized scenarios before launching the
 command; it never clamps the requested dimensions. This limit is independent
diff --git a/src/domain/process/processScenario.terminalCompatibility.test.ts b/src/domain/process/processScenario.terminalCompatibility.test.ts
new file mode 100644
index 0000000000..1459dfbf17
--- /dev/null
+++ b/src/domain/process/processScenario.terminalCompatibility.test.ts
@@ -0,0 +1,21 @@
+import { expect, it } from "vitest";
+
+import { EMPTY_PROCESS_CAPTURE_EXAMPLE } from "./processCaptureExample.js";
+import { parseProcessCapture } from "./processCaptureParsing.js";
+import { digestProcessCommitment } from "./processScenario.js";
+
+it("retains a previously recorded one-column scenario in process Evidence", () => {
+  const scenario = {
+    ...EMPTY_PROCESS_CAPTURE_EXAMPLE.manifest.scenario,
+    terminal: { columns: 1, rows: 2, scrollback: 0 },
+  };
+  const capture = {
+    ...EMPTY_PROCESS_CAPTURE_EXAMPLE,
+    manifest: {
+      ...EMPTY_PROCESS_CAPTURE_EXAMPLE.manifest,
+      scenario,
+      full_scenario_sha256: digestProcessCommitment(scenario),
+    },
+  };
+  expect(parseProcessCapture(capture).manifest.scenario).toEqual(scenario);
+});
diff --git a/src/domain/process/processScenario.test.ts b/src/domain/process/processScenario.test.ts
index 3aa5a00664..2c2e1e5c80 100644
--- a/src/domain/process/processScenario.test.ts
+++ b/src/domain/process/processScenario.test.ts
@@ -189,9 +189,9 @@ it("admits the default and the exact combined terminal-cell budget", () => {
     processScenarioSchema.safeParse({
       executable: "/bin/true",
       terminal: {
-        columns: 1,
+        columns: 2,
         rows: 1,
-        scrollback: PROCESS_TERMINAL_CELL_BUDGET - 1,
+        scrollback: PROCESS_TERMINAL_CELL_BUDGET / 2 - 1,
       },
     }).success,
   ).toBe(true);
@@ -250,7 +250,7 @@ it("applies the selected scrollback budget to every scheduled resize", () => {
   expect(
     processScenarioSchema.safeParse({
       executable: "/bin/true",
-      terminal: { columns: 1, rows: 1, scrollback: 0 },
+      terminal: { columns: 2, rows: 1, scrollback: 0 },
       events: [{ type: "resize", at_ms: 10, columns: 1_000, rows: 1 }],
     }).success,
   ).toBe(true);
diff --git a/src/domain/process/processScenario.ts b/src/domain/process/processScenario.ts
index 1a867034dd..0bafd5c163 100644
--- a/src/domain/process/processScenario.ts
+++ b/src/domain/process/processScenario.ts
@@ -14,6 +14,8 @@ export const processScenarioOutputBudgetProjectionSchema = z
  * before row objects, serialization strings, and retained frame copies.
  */
 export const PROCESS_TERMINAL_CELL_BUDGET = 1_000_000;
+/** The pinned xterm renderer cannot represent a one-column terminal. */
+export const PROCESS_TERMINAL_MIN_COLUMNS = 2;
 const timedEventBase = { at_ms: z.int().safe().nonnegative() };
 const reservedRunIdEnvironmentName = "REA_PROCESS_RUN_ID";
 const ENVIRONMENT_NAME_CHARACTER = "[^=\\x00]";
@@ -186,12 +188,16 @@ export const processScenarioSchema = z
       .default([]),
     terminal: z
       .strictObject({
-        columns: z.int().min(1).max(65_535).default(80),
+        columns: z
+          .int()
+          .min(PROCESS_TERMINAL_MIN_COLUMNS)
+          .max(65_535)
+          .default(80),
         rows: z.int().min(1).max(65_535).default(24),
         scrollback: z.int().safe().nonnegative().default(1_000),
       })
       .describe(
-        "The visible terminal and scrollback together must use at most 1,000,000 xterm renderer cells: columns × (rows + scrollback). Resize events use the same scrollback and limit. This release has no runtime override.",
+        "The renderer requires at least 2 columns. The visible terminal and scrollback together must use at most 1,000,000 xterm renderer cells: columns × (rows + scrollback). Resize events use the same minimum width, scrollback and limit. This release has no runtime override.",
       )
       .default({ columns: 80, rows: 24, scrollback: 1_000 }),
     events: z
@@ -206,7 +212,7 @@ export const processScenarioSchema = z
           z.strictObject({
             ...timedEventBase,
             type: z.literal("resize"),
-            columns: z.int().min(1).max(65_535),
+            columns: z.int().min(PROCESS_TERMINAL_MIN_COLUMNS).max(65_535),
             rows: z.int().min(1).max(65_535),
           }),
           z.strictObject({
diff --git a/tests/acceptance/process/processTerminalWidth.test.ts b/tests/acceptance/process/processTerminalWidth.test.ts
new file mode 100644
index 0000000000..221756a8dd
--- /dev/null
+++ b/tests/acceptance/process/processTerminalWidth.test.ts
@@ -0,0 +1,83 @@
+import { access, writeFile } from "node:fs/promises";
+import { join } from "node:path";
+import { Ajv2020 } from "ajv/dist/2020.js";
+import { expect } from "vitest";
+
+import { parseEvidence } from "../../../src/domain/evidence.js";
+import { parseProcessCapture } from "../../../src/domain/process/processCaptureParsing.js";
+import { CAPTURE_SKIP_REASON } from "../../boundary/process/processCaptureCapability.js";
+import { connectLocalToolsMcp } from "../../fixtures/localToolsMcp.js";
+import { createTestTempDirectory } from "../../fixtures/temporaryDirectory.js";
+import { cliTest } from "../../support/cli/cliFixture.js";
+
+cliTest(
+  "rejects one-column capture and resize before starting the target",
+  async ({ cli }) => {
+    const root = await createTestTempDirectory("rea-process-width-");
+    const marker = join(root, "launched");
+    const base = {
+      executable: process.execPath,
+      arguments: [
+        "-e",
+        `require('fs').writeFileSync(${JSON.stringify(marker)}, 'started')`,
+      ],
+      terminal: { columns: 2, rows: 2, scrollback: 0 },
+    };
+    const scenarios = [
+      { ...base, terminal: { ...base.terminal, columns: 1 } },
+      { ...base, events: [{ type: "resize", at_ms: 0, columns: 1, rows: 2 }] },
+    ];
+    const { client, call } = await connectLocalToolsMcp();
+    const definition = (await client.listTools()).tools.find(
+      ({ name }) => name === "capture_process_scenario",
+    );
+    expect(definition).toBeDefined();
+    const validate = new Ajv2020({ strict: false }).compile(
+      definition!.inputSchema,
+    );
+    for (const [index, scenario] of scenarios.entries()) {
+      expect(validate(scenario)).toBe(false);
+      expect((await call("capture_process_scenario", scenario)).isError).toBe(
+        true,
+      );
+      const path = join(root, `scenario-${String(index)}.json`);
+      await writeFile(path, JSON.stringify(scenario));
+      const result = await cli.run({
+        arguments: ["capture-process", path, "--json"],
+      });
+      expect(result.exitCode).toBe(1);
+      expect(result.json).toMatchObject({ code: "invalid_request" });
+      await expect(access(marker)).rejects.toMatchObject({ code: "ENOENT" });
+    }
+    expect(validate(base)).toBe(true);
+  },
+);
+
+cliTest.skipIf(CAPTURE_SKIP_REASON)(
+  "retains the requested two-column screen through capture and resize",
+  async ({ cli }) => {
+    const root = await createTestTempDirectory("rea-process-width-control-");
+    const path = join(root, "scenario.json");
+    await writeFile(
+      path,
+      JSON.stringify({
+        executable: process.execPath,
+        arguments: ["-e", "process.stdout.write('ab');setTimeout(()=>{}, 100)"],
+        terminal: { columns: 2, rows: 2, scrollback: 0 },
+        events: [{ type: "resize", at_ms: 20, columns: 2, rows: 2 }],
+        timeout_ms: 5_000,
+      }),
+    );
+    const result = await cli.run({
+      arguments: ["capture-process", path, "--json"],
+    });
+    expect(result.exitCode, result.stderr).toBe(0);
+    const capture = parseProcessCapture(
+      parseEvidence(result.json).normalized_result,
+    );
+    expect(capture.rendered_frames.length).toBeGreaterThan(0);
+    expect(capture.rendered_frames.every((frame) => frame.columns === 2)).toBe(
+      true,
+    );
+  },
+);