fix: insert paths and task input verbatim at placeholder substitutions

packages/coding-agent/changelog.d/replacement-pattern-paths.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- Paths and task input are now inserted verbatim where GJC substitutes a placeholder. Five call sites passed a variable as the replacement argument of `String.prototype.replace`/`replaceAll`, so JavaScript expanded `$&`, `$$`, `` $` `` and `$'` inside the value instead of copying it: a plugin installed under `a$&b` launched its MCP server from `a${CLAUDE_PLUGIN_ROOT}b/...`, a repository named `q$'z` had its launch worktrees resolved to `q/.worktreesz/.worktrees`, and a workflow command run with `sed s/a/$&/g` received `sed s/a/$@/g`. Affected: plugin MCP `command`/`args`/`env`/`cwd` root substitution, the launch-worktree bucket and coordinator managed-worktree `{repo}` templates, `~` expansion for `gjc auth-broker import`, and `$@` in workflow command instructions.

packages/coding-agent/src/cli/auth-broker-cli.ts

@@ -467,7 +467,7 @@ async function runImport(flags: AuthBrokerCommandArgs["flags"]): Promise<void> {
 	if (!target) {
 		throw new Error("Usage: gjc auth-broker import <file|dir> [--provider=<id>] [--include-disabled] [--dry-run]");
 	}
-	const resolvedTarget = path.resolve(target.startsWith("~") ? target.replace(/^~/, os.homedir()) : target);
+	const resolvedTarget = path.resolve(target.startsWith("~") ? target.replace(/^~/, () => os.homedir()) : target);
 	const { entries, skipped } = await loadImportPlan(resolvedTarget, flags.provider, flags.includeDisabled === true);
 
 	if (flags.json) {

packages/coding-agent/src/coordinator-mcp/policy.ts

@@ -122,8 +122,9 @@ function parseRootList(value: string | undefined): string[] {
 }
 
 function resolveManagedWorktreeRoot(root: string, configured: string | undefined): string {
-	const template = (configured?.trim() || "{repo}/.worktrees").replace(/^~(?=\/|$)/, os.homedir());
-	const resolved = template.replaceAll("{repo}", path.basename(root));
+	// Function replacers so a `$` in the home or repository path is kept verbatim.
+	const template = (configured?.trim() || "{repo}/.worktrees").replace(/^~(?=\/|$)/, () => os.homedir());
+	const resolved = template.replaceAll("{repo}", () => path.basename(root));
 	return path.resolve(path.isAbsolute(resolved) ? resolved : path.join(path.dirname(root), resolved));
 }
 

packages/coding-agent/src/discovery/substitute-plugin-root.ts

@@ -8,7 +8,9 @@ const GJC_VAR = "$" + "{GJC_PLUGIN_ROOT}";
 
 export function substitutePluginRoot<T>(value: T, rootPath: string): T {
 	if (typeof value === "string") {
-		return value.replaceAll(CLAUDE_VAR, rootPath).replaceAll(GJC_VAR, rootPath) as T;
+		// Function replacers: a string replacement would expand `$&`, `$$`, `` $` ``
+		// and `$'` inside the install path instead of inserting it verbatim.
+		return value.replaceAll(CLAUDE_VAR, () => rootPath).replaceAll(GJC_VAR, () => rootPath) as T;
 	}
 	if (Array.isArray(value)) {
 		return value.map(v => substitutePluginRoot(v, rootPath)) as T;

packages/coding-agent/src/gjc-runtime/launch-worktree.ts

@@ -205,7 +205,8 @@ export function resolveWorktreeBucketForPath(
 	const template = expandHomePrefix(configured || DEFAULT_WORKTREE_BUCKET, home, pathApi);
 	return pathApi.resolve(
 		pathApi.dirname(repoRoot),
-		template.replaceAll(REPO_NAME_PLACEHOLDER, pathApi.basename(repoRoot)),
+		// Function replacer so a `$` in the repository directory name is kept verbatim.
+		template.replaceAll(REPO_NAME_PLACEHOLDER, () => pathApi.basename(repoRoot)),
 	);
 }
 

packages/coding-agent/src/task/commands.ts

@@ -120,7 +120,9 @@ export function getCommand(commands: WorkflowCommand[], name: string): WorkflowC
  * Replaces $@ with the provided input.
  */
 export function expandCommand(command: WorkflowCommand, input: string): string {
-	return command.instructions.replace(/\$@/g, input);
+	// Function replacer: `input` is user text and must be inserted verbatim, not
+	// parsed for `$&`, `$$`, `` $` `` or `$'` replacement patterns.
+	return command.instructions.replace(/\$@/g, () => input);
 }
 
 /**

packages/coding-agent/test/coordinator-mcp-policy.test.ts

@@ -152,6 +152,16 @@ describe("Hermes MCP safety policy", () => {
 		await expect(assertCoordinatorWorkdir(config, worktree)).resolves.toBe(worktree);
 	});
 
+	it("derives the managed worktree root from a repository name containing replacement-pattern characters", () => {
+		// `{repo}` used a string replacement, so `$&` in the directory name expanded to
+		// the placeholder itself and `$'` spliced the template remainder into the path.
+		for (const name of ["a$&b", "x$$y", "q$'z"]) {
+			const root = path.join(os.tmpdir(), name);
+			const config = buildCoordinatorMcpConfig({ GJC_COORDINATOR_MCP_WORKDIR_ROOTS: root });
+			expect(config.managedWorktreeRoots).toEqual([path.join(root, ".worktrees")]);
+		}
+	});
+
 	it("rejects artifact symlink escapes and enforces byte caps", async () => {
 		const root = await tempRoot();
 		const outside = await tempRoot();

packages/coding-agent/test/gjc-runtime/launch-worktree.test.ts

@@ -773,6 +773,19 @@ describe("GJC_WORKTREE_DIR path red-team", () => {
 	});
 });
 
+describe("resolveWorktreeBucketForPath repository names with replacement-pattern characters", () => {
+	// `{repo}` was substituted with a string replacement, so `$&`, `$$`, `` $` `` and
+	// `$'` in the directory name were expanded: `a$&b` resolved to `a{repo}b`, and
+	// `q$'z` spliced the template remainder into the path.
+	for (const name of ["a$&b", "x$$y", "x$`y", "q$'z", "$1"]) {
+		it(`keeps ${JSON.stringify(name)} verbatim`, () => {
+			const repo = `/src/${name}`;
+			expect(resolveWorktreeBucketForPath(repo, undefined, "/home/u", path.posix)).toBe(`/src/${name}/.worktrees`);
+			expect(resolveWorktreeBucketForPath(repo, "~/wt/{repo}", "/home/u", path.posix)).toBe(`/home/u/wt/${name}`);
+		});
+	}
+});
+
 describe("resolveWorktreeBucketForPath Windows semantics", () => {
 	const home = "C:\\Users\\kim";
 	const repo = "C:\\repos\\app";

packages/coding-agent/test/marketplace/substitute-plugin-root.test.ts

@@ -56,4 +56,14 @@ describe("substitutePluginRoot", () => {
 	it("returns string unchanged when no variables present", () => {
 		expect(substitutePluginRoot("no-vars-here", ROOT)).toBe("no-vars-here");
 	});
+	it("inserts an install path containing replacement-pattern characters verbatim", () => {
+		// A string replacement would expand `$&`, `$$`, `` $` `` and `$'` inside the
+		// path: `a$&b` became `a${CLAUDE_PLUGIN_ROOT}b`, `x$`y` lost `$`y`, and `q$'z`
+		// spliced the remainder of the template into the middle of the path.
+		for (const root of ["/plugins/a$&b", "/plugins/x$$y", "/plugins/x$`y", "/plugins/q$'z", "/plugins/$1"]) {
+			expect(substitutePluginRoot(`${CLAUDE_VAR}/bin/server`, root)).toBe(`${root}/bin/server`);
+			expect(substitutePluginRoot(`${GJC_VAR}/bin/server`, root)).toBe(`${root}/bin/server`);
+			expect(substitutePluginRoot([`--config=${CLAUDE_VAR}/c.json`], root)).toEqual([`--config=${root}/c.json`]);
+		}
+	});
 });

packages/coding-agent/test/task/expand-command.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from "bun:test";
+import { expandCommand, type WorkflowCommand } from "../../src/task/commands";
+
+function command(instructions: string): WorkflowCommand {
+	return { name: "review", description: "", instructions, source: "user", filePath: "/tmp/review.md" };
+}
+
+describe("expandCommand", () => {
+	it("substitutes every $@ with the task input", () => {
+		expect(expandCommand(command("Review:\n$@\nThen re-check $@."), "the login fix")).toBe(
+			"Review:\nthe login fix\nThen re-check the login fix.",
+		);
+	});
+
+	it("inserts input containing replacement-pattern characters verbatim", () => {
+		// The input was passed as a string replacement, so `$&` became `$@`, `$$`
+		// collapsed to `$`, and `` $` `` / `$'` spliced the instructions before or
+		// after the placeholder into the user's text.
+		for (const input of ["sed s/a/$&/g", "costs $$5", "regex /^$`/", "the $' suffix", "awk '{print $1}'"]) {
+			expect(expandCommand(command("Task: $@ (done)"), input)).toBe(`Task: ${input} (done)`);
+		}
+	});
+});