[Bug] expandTildePath produces mixed path separators on Windows

[RelaxJonh]

Affected area

Coding agent and CLI (Windows)

What happened?

expandTildePath() in packages/coding-agent/src/config.ts (line 515) uses string concatenation instead of path.join, producing mixed path separators on Windows:

export function expandTildePath(path: string): string {
    if (path === "~") return homedir();
    if (path.startsWith("~/")) return homedir() + path.slice(1);
    return path;
}

On Windows, homedir() returns C:\Users\username (backslashes). When the input is ~/something, the result is C:\Users\username/something — mixing \ and / separators.

This function is called by getAgentDir() (line 537) and getSessionDir() (line 658) when PRIME_AGENT_CODING_AGENT_DIR or PRIME_AGENT_SESSION_DIR environment variables are set with a tilde prefix.

Steps to reproduce

On Windows:

1. Set PRIME_AGENT_CODING_AGENT_DIR=~/my-agent
2. Call getAgentDir()
3. Observe the returned path contains mixed separators: C:\Users\username/my-agent

Compare with the default path (no env var set), which uses join(homedir(), CONFIG_DIR_NAME) and produces C:\Users\username\.prime\agent (consistent backslashes).

Expected behavior

expandTildePath should return a path with consistent separators, matching the behavior of path.join. Either:

• Use join(homedir(), path.slice(2)) after the ~/ check, or
• Normalize the result with path.normalize()

Actual behavior

Mixed separators in paths derived from environment variables. While Node.js fs functions generally handle mixed separators, some external tools, string comparisons, and path equality checks may not. The inconsistency between env-var-derived paths (mixed) and default paths (normalized) can cause subtle bugs in path comparison logic.

Impact

• Path comparisons like getAgentDir() === someOtherPath may fail when both refer to the same directory
• External tools that receive these paths may behave unexpectedly
• Log messages and error reports show inconsistent path formats

Suggested fix

import { join, normalize } from "node:path";

export function expandTildePath(inputPath: string): string {
    if (inputPath === "~") return homedir();
    if (inputPath.startsWith("~/")) return join(homedir(), inputPath.slice(2));
    return inputPath;
}

Prime Agent version

0.7.2 (source checkout at main)

Environment

Windows 11, Node.js 24.x