diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 10a4dfc56..8e6402af0 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -115,6 +115,7 @@
 - Fixed prompt templates discovered from `cwd/.omp/prompts/` and the agent prompts directory not appearing in the slash-command autocomplete picker. `InteractiveMode.refreshSlashCommandState()` now feeds `session.promptTemplates` into the autocomplete provider alongside builtins and file-based slash commands; templates whose names collide with an existing command are skipped to mirror the runtime expansion order (`expandSlashCommand` precedes `expandPromptTemplate`) ([#2462](https://github.com/can1357/oh-my-pi/issues/2462)).
 - Fixed empty-Enter steering interrupts leaving the newest queued steer visible after aborting an auto-continued queued turn; queued turns now re-drain after every abort/settle cycle.
 - Added an agent-visible notice when the write tool auto-marks shebang files executable, so agents do not redundantly run `chmod +x`.
+- Fixed unknown `--`-prefixed flags being silently consumed as prompt text, which let a stale or typoed flag start a real agent session (connecting to MCP servers, waiting on the model) instead of failing fast. `parseArgs` now tracks unrecognized flag-shaped tokens and `runRootCommand` calls `reportUnrecognizedFlags` immediately after the post-extension reparse, exiting `2` with `Error: unknown flag: --…` before any session, MCP, or initial-message work runs. Extension-registered flags still pass cleanly since the validation runs after the extension-aware reparse, and `--` is honored as a POSIX positional separator so flag-shaped prompts (`omp -p -- --explain-this`) survive the new guard ([#2459](https://github.com/can1357/oh-my-pi/issues/2459)).
 
 ## [15.12.4] - 2026-06-13
 
diff --git a/packages/coding-agent/src/cli/args.ts b/packages/coding-agent/src/cli/args.ts
index 704a96740..ef0dffa72 100644
--- a/packages/coding-agent/src/cli/args.ts
+++ b/packages/coding-agent/src/cli/args.ts
@@ -81,10 +81,20 @@ export function parseArgs(inputArgs: string[], extensionFlags?: Map<string, { ty
 		unrecognizedFlags: [],
 	};
 
+	let sawSeparator = false;
 	for (let i = 0; i < args.length; i++) {
 		let arg = args[i];
 		const flagIndex = i;
 
+		// POSIX positional separator: once `--` lands, every remaining token is
+		// a positional regardless of shape. Without this, a flag-looking message
+		// (`omp -p -- --explain-this`) would be re-validated by the loop below
+		// and rejected by the unknown-flag guard (#2461 review).
+		if (sawSeparator) {
+			result.messages.push(arg);
+			continue;
+		}
+
 		// Support --flag=value syntax (e.g. --tools=ask,read). The value is
 		// spliced in as the next token so value-consuming flags pick it up via
 		// `args[++i]`; a non-consuming flag (e.g. a boolean) leaves it behind and
@@ -241,10 +251,15 @@ export function parseArgs(inputArgs: string[], extensionFlags?: Map<string, { ty
 			result.skills = args[++i].split(",").map(s => s.trim());
 		} else if (arg.startsWith("@")) {
 			result.fileArgs.push(arg.slice(1)); // Remove @ prefix
-		} else if (!arg.startsWith("-") || arg === "-" || arg === "--") {
-			// Plain positional, lone `-` (stdin marker), or POSIX positional
-			// separator `--` — pass through as a message rather than flagging it.
-			if (arg !== "--") result.messages.push(arg);
+		} else if (!arg.startsWith("-") || arg === "-") {
+			// Plain positional or lone `-` (stdin marker) — pass through as a
+			// message rather than flagging it.
+			result.messages.push(arg);
+		} else if (arg === "--") {
+			// POSIX positional separator: drop the token and switch the loop
+			// into "everything from here is a positional" mode. The guard at
+			// the top of the loop body handles the remaining tokens.
+			sawSeparator = true;
 		} else {
 			// Flag-shaped (`-x`, `--name`) but unrecognized at this parse. Record
 			// it so the post-extension reparse can decide whether to surface it
diff --git a/packages/coding-agent/test/cli-unknown-flag.test.ts b/packages/coding-agent/test/cli-unknown-flag.test.ts
index c5bf189d5..ba142dcf8 100644
--- a/packages/coding-agent/test/cli-unknown-flag.test.ts
+++ b/packages/coding-agent/test/cli-unknown-flag.test.ts
@@ -66,6 +66,25 @@ describe("parseArgs — unrecognized flag tracking (#2459)", () => {
 		expect(ddash.messages).toEqual(["hello"]);
 	});
 
+	it("treats every token after `--` as a positional, even flag-shaped ones (#2461 review)", () => {
+		// `omp -p -- --explain-this` must forward `--explain-this` as the
+		// prompt body. Without after-separator semantics the unknown-flag guard
+		// trips on it and the CLI exits before any session work.
+		const parsed = parseArgs(["-p", "--", "--explain-this", "-x", "plain"]);
+		expect(parsed.print).toBe(true);
+		expect(parsed.unrecognizedFlags).toEqual([]);
+		expect(parsed.messages).toEqual(["--explain-this", "-x", "plain"]);
+	});
+
+	it("does not expand `@foo` after `--` into a fileArg (POSIX positional semantics)", () => {
+		// After `--`, application-level conventions like `@file` no longer
+		// apply — the token is a literal positional. Lets users include `@`
+		// strings (e.g. emails, handles) in prompts without file lookup.
+		const parsed = parseArgs(["--", "@notes.md", "hello"]);
+		expect(parsed.fileArgs).toEqual([]);
+		expect(parsed.messages).toEqual(["@notes.md", "hello"]);
+	});
+
 	it("clears extension-registered flags from unrecognizedFlags on the post-extension reparse", () => {
 		const argv = ["--spawn-peer", "reviewer", "review the diff"];