docs: correct the .env.local readability claim

The file-read tool denies every .env.* path via .claude/settings.json, .env.local included, so the section points at cat instead of implying the file is readable.

DATABASE_URL carries an export prefix, which the bare 'source .env.local' in .envrc needs to reach cargo and sqlx, and which a ^DATABASE_URL= grep would miss. Documented rather than removed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

AGENTS.md

@@ -79,7 +79,9 @@ checkout with nothing running.
 
 **`.env.local` in the worktree root is the portable answer** — `BACKEND_PORT`,
 `FRONTEND_PORT`, `REMOTE`, `DATABASE_URL`, `CARGO_FEATURES`, `WM_DB_NAME`. Both managers write
-those fields, so it is correct whichever one you are in, and it is readable despite the name.
+those fields, so it is correct whichever one you are in. Read it with `cat .env.local` from a
+shell: the file-read tool denies every `.env.*` path, and `DATABASE_URL` is written with an
+`export` prefix that a `^DATABASE_URL=` grep misses.
 
 webmux additionally writes `$(git rev-parse --git-dir)/webmux/runtime.env`, which every pane
 sources at startup and which carries the extras `.env.local` lacks: `WEBMUX_*`, `WM_CLONE_DB`,

scripts/worktree-common.sh

@@ -13,8 +13,7 @@ wm_main_repo_root() {
   cd "$(git -C "$repo_root" rev-parse --git-common-dir 2>/dev/null)/.." && pwd
 }
 
-# Written by both worktree entry points — `worktree-env` by hand, `post-create.sh` from the
-# webmux hook — and read by agents to find their own ports, so the two must not drift.
+# These field names are documented in AGENTS.md as how an agent finds its own ports and database.
 wm_write_env_local() {
   local repo_root=$1
   local backend_port=$2