diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index e1e5aab1e..646231915 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -99,6 +99,7 @@
 - Fixed `/live` sideband WebSockets ignoring standard proxy environment variables and `NO_PROXY`, which left proxied sessions stuck while the rest of the Codex connection succeeded ([#6770](https://github.com/can1357/oh-my-pi/issues/6770)).
 - Fixed the bash tool's `kill` builtin rejecting numeric signals and multiple process operands, stopping after the first failed target, and defaulting to `SIGKILL` instead of the standard `SIGTERM`. Negative PID operands (process groups per `kill(2)`) and the `--` end-of-options marker are now handled instead of being misparsed as signals ([#6779](https://github.com/can1357/oh-my-pi/issues/6779)).
 - Fixed `learned.md` saves growing a blank line on every write (trailing-newline split artifact) and hoisting all headings/prose above all bullets, which re-scoped lessons under the wrong heading in hand-organized files. Saves are now byte-idempotent and preserve mixed Markdown ordering: non-list lines keep their positions, new lessons insert newest-first at the head of the first bullet run, and dedupe/cap operate on bullet lines in place.
+- Fixed the `write` tool treating a semicolon-joined list of read selectors (e.g. `a.txt:1-2;b/c.txt:3-4`) as a filesystem path, silently creating a nested directory tree when a read-only step mis-dispatched a multi-file `read` as `write`. Such targets are now refused regardless of `content`, since no real write targets a `;`-list whose every segment carries a read selector ([#6809](https://github.com/can1357/oh-my-pi/issues/6809)).
 
 ## [17.1.5] - 2026-07-27
 
diff --git a/packages/coding-agent/src/tools/write.ts b/packages/coding-agent/src/tools/write.ts
index ede959518..e7ff239f0 100644
--- a/packages/coding-agent/src/tools/write.ts
+++ b/packages/coding-agent/src/tools/write.ts
@@ -160,7 +160,38 @@ function throwReadSelectorMisfire(target: string, sel: string): never {
 	);
 }
 
+/**
+ * Recognize a semicolon-joined list of read-tool selectors mis-dispatched as a
+ * single write target — the multi-file read expression the scout emitted in
+ * issue #6809 (`a.txt:1-2;b/c.txt:3-4`). Every `;`-segment must be non-empty and
+ * carry its own read selector ({@link splitPathAndSel} peels a `:N-M`, `:raw`,
+ * or `:conflicts` tail). No real call targets such a list: `read` accepts one
+ * path, `write` writes one file. Unlike {@link readSelectorForEmptyWrite} this
+ * fires regardless of `content` — the non-empty-content escape hatch exists for
+ * a lone selector-shaped *filename*, never a `;`-list, and honoring it here
+ * silently creates a nested directory tree (`a.txt:1-2;b/`) in the workspace.
+ */
+function readSelectorListMisfire(target: string): number | undefined {
+	if (!target.includes(";")) return undefined;
+	const segments = target.split(";");
+	if (segments.length < 2) return undefined;
+	for (const segment of segments) {
+		const trimmed = segment.trim();
+		if (trimmed.length === 0 || splitPathAndSel(trimmed).sel === undefined) return undefined;
+	}
+	return segments.length;
+}
+
+function throwReadSelectorListMisfire(target: string, count: number): never {
+	throw new ToolError(
+		`write target '${target}' is a semicolon-joined list of ${count} read-tool selectors, not a filesystem path — refusing to create it. ` +
+			`write creates a single file; issue one read() per path to read these ranges (e.g. read({ path: "<one path>:<range>" })).`,
+	);
+}
+
 async function assertNotReadSelectorMisfire(target: string, content: string, cwd: string): Promise<void> {
+	const listCount = readSelectorListMisfire(target);
+	if (listCount !== undefined) throwReadSelectorListMisfire(target, listCount);
 	const sel = readSelectorForEmptyWrite(target, content);
 	if (sel === undefined) return;
 	if ((await probeLiteralPathExists(target, cwd)) !== "missing") return;
diff --git a/packages/coding-agent/test/write-read-selector-misfire.test.ts b/packages/coding-agent/test/write-read-selector-misfire.test.ts
index 917ba7482..ea5192844 100644
--- a/packages/coding-agent/test/write-read-selector-misfire.test.ts
+++ b/packages/coding-agent/test/write-read-selector-misfire.test.ts
@@ -103,4 +103,27 @@ describe("write refuses read-selector misfires", () => {
 		expect(entries.get(member)).toEqual(new Uint8Array());
 		await fs.rm(dir, { recursive: true, force: true });
 	});
+
+	it("rejects a semicolon-joined selector list with non-empty content and creates nothing", async () => {
+		const dir = await makeWorkspace();
+		const write = new WriteTool(session(dir));
+		const target = "a.txt:1-2;b/c.txt:3-4";
+		await expect(write.execute("c", { path: target, content: "{}" })).rejects.toThrow(
+			/semicolon-joined list of 2 read-tool selectors/,
+		);
+		expect(await Bun.file(path.join(dir, target)).exists()).toBe(false);
+		expect(await Bun.file(path.join(dir, "a.txt:1-2;b/c.txt:3-4")).exists()).toBe(false);
+		expect(await fs.readdir(dir)).toEqual(["src"]);
+		await fs.rm(dir, { recursive: true, force: true });
+	});
+
+	it("still writes a real path that merely contains a semicolon (no per-segment selectors)", async () => {
+		const dir = await makeWorkspace();
+		const write = new WriteTool(session(dir));
+		const target = "notes;draft.txt";
+		const res = await write.execute("c", { path: target, content: "hi" });
+		expect(res.isError).toBeUndefined();
+		expect(await Bun.file(path.join(dir, target)).text()).toBe("hi");
+		await fs.rm(dir, { recursive: true, force: true });
+	});
 });