devenv broken on megarepo worktrees with %2F in path

Problem

devenv shell / direnv exec . fails on megarepo worktrees where branch names containing / get encoded as %2F in the filesystem path, e.g.:

.megarepo/.../refs/heads/schickling%2F2026-02-10-otel-dash-provisioning

This prevents running dt ts:check, dt lint:check, or any devenv-dependent command locally on these worktrees.

Root cause

Two bugs in devenv when the working directory contains literal %:

1. SQLx URL parser in devenv-cache-core/src/db.rs percent-decodes %2F → / in the SQLite connection string, causing it to try opening the DB at a non-existent path (SQLite error 14)
2. Nix expression parser rejects % as an invalid token in import paths

Upstream

• Filed: cachix/devenv#2492
• Reproduction: https://github.com/schickling-repros/2026-02-devenv-percent-encoded-path

Workaround options

1. Megarepo: Use real directory hierarchy (schickling/branch-name/) instead of URL-encoded flat names — older worktrees already use this pattern
2. Symlink: Create a symlink without %2F pointing to the worktree
3. Wait for upstream fix in devenv

Context

• CI is unaffected (checks out fresh without %2F paths)
• Only impacts local development on these worktrees
• Older worktrees using real / directory separators work fine

Acting on behalf of @schickling via CLI assistant.

Reproduce the failure with devenv shell or direnv exec . from a megarepo worktree whose path contains %2F. Read the linked upstream devenv issue and reproduction, then determine whether an upstream fix is available; the issue is done only when affected local devenv-dependent commands work without a workaround.