v0.2.0.0 feat: sync gradle.properties keys via .secrets-files (EGB-531)

Add a committed .secrets-files manifest that lets secrets track designated
keys from files outside the project root (motivating case:
~/.gradle/gradle.properties for Android Clerk publishable keys, which
Android Studio GUI builds read but terminal env vars can't reach).

- push extracts only the named keys, encrypts under <project>/external/
- pull MERGES them into the target, preserving unrelated keys/comments/order
- pure-bash merge (no sed/regex): exact-string key match, opaque values
- path validator: basename gradle.properties, within $HOME, no symlink/..
- external/ subdir keeps blobs out of the dotenv *.age globs; rekey + list
  recurse explicitly
- which reads back the manifest; list shows [external]; pre-commit blocks
  plaintext gradle.properties

Also fixes two latent bugs in 'secrets rekey' (never completed before, no
prior test): age-keygen refusing to overwrite key.txt, and an EXIT trap
referencing an out-of-scope local under set -u.

Tests: 80 -> 104.

Reviewed via /autoplan (CEO/Eng/DX). EGB-531.

CLAUDE.md

@@ -26,16 +26,18 @@ Single bash script (`secrets`) with subcommands: init, push, pull, list, rm, rek
 - Encryption: `age` with key files (not passphrases — age passphrases are non-scriptable)
 - Storage: Private git repo at `~/.secrets/`
 - Convention: Tracks `.env`, `.env.*`, and `.dev.vars` (not `.envrc`, `.environment-*`)
+- External files: `.secrets-files` manifest tracks designated keys from files outside the project (e.g. `~/.gradle/gradle.properties`) — merged, not overwritten (EGB-531, see below)
 - Workspaces: `--workspaces` flag reads `package.json` workspaces, requires `jq`
-- Safety: Pre-commit hook rejects plaintext secret files
+- Safety: Pre-commit hook rejects plaintext secret files (`.env`, `.dev.vars`, `gradle.properties`)
+- Portability: must run on system bash 3.2 (macOS) — no associative arrays or bash-4 features
 
 ## Project Structure
 
 ```
-secrets              # CLI script (~300 lines bash)
+secrets              # CLI script (~600 lines bash)
 hooks/pre-commit     # Pre-commit hook template
 test/
-  secrets.bats       # bats-core test suite (25 tests)
+  secrets.bats       # bats-core test suite (104 tests)
   test_helper.bash   # Shared setup/teardown
 README.md            # User-facing documentation
 CLAUDE.md            # This file
@@ -58,6 +60,19 @@ The active store directory is picked by `resolve_store()` using these rules, hig
 
 `.secrets-store` parsing is deliberately conservative: first non-empty non-comment line wins, no shell expansion (no `$VAR`, `$()`, backticks). Bare names map via `_expand_store_path`: `work` → `$HOME/.secrets-work`, `default` → `$HOME/.secrets`. An optional remote URL after the spec on the same line is captured as `_REMOTE_URL` and passed through to `check_initialized`, which uses it to fill in a runnable `git clone <url> <path>` in the missing-store error (EGB-282). The URL is parsed via `read -r spec rest` (no `set -- $line`, no glob expansion) and then **sanitized**: any URL containing shell metacharacters (`;&|<>$\`(){}*?!"'\\`), control characters (incl. ANSI escapes), or whitespace is dropped with a stderr warning. The directed error then falls back to the `<their-store-remote>` placeholder. This matters because the rendered `git clone` line is meant to be copy-pasted by a teammate — without sanitization, `work evil.git;rm -rf ~` would render verbatim and execute the payload on paste. Internal flow: `_parse_secrets_store_file` returns `<spec>\t<url>`; `_find_secrets_store_file` returns `<dir>\t<source-path>\t<url>`; `resolve_store` splits the 3-tuple via `IFS=$'\t' read -r ...`.
 
+## External files (.secrets-files) — EGB-531
+
+`.secrets-files` is a committed, project-root manifest declaring keys to sync from files **outside** the project (motivating case: `~/.gradle/gradle.properties`, which Android Studio GUI builds read but terminal env vars can't reach). One entry per line: `<type> <path> <key>...`. Only type `gradle-properties` is supported; the type token leaves room for future types **without** a plugin-dispatch framework (build the concrete case — a deliberate scope cut).
+
+Key design decisions (all driven by /autoplan review):
+
+- **Wire-in is at command scope** (`cmd_push`/`cmd_pull`), via `push_external_files` / `pull_external_files`, **not** inside `push_dir_to_project` / `pull_project_to_dir` (those loop per-workspace and `pull_project_to_dir` uses stdout as a data channel).
+- **Storage:** blobs live in `$SECRETS_DIR/<project>/external/<slug>.gradle-properties.age`. The `external/` subdir keeps them out of the existing non-recursive `*.age` / `.*.age` globs (pull, list, rekey), so the old dotenv path can never decrypt a blob into cwd. `cmd_rekey` and `cmd_list` recurse into `external/` explicitly (rekey MUST, or the blob is orphaned after rotation = data loss). `<slug>` = manifest path token with non-`[A-Za-z0-9._-]` chars → `_`, so it's machine-independent.
+- **Merge is pure bash, no `sed`/regex** (`merge_gradle_keys`): exact-string key comparison (avoids `beaconClerkPk` vs `beaconClerkPkTest` substring bug), value treated as opaque literal (survives `& \ /` in values). Updates a managed key in place at its first occurrence, collapses duplicates, appends new keys, preserves unrelated lines/comments/order. Continuation lines (trailing odd backslashes, tracked by `_trailing_bs_odd`) are never matched as keys. Atomic write: temp in the same dir → `chmod` to match (or `600` on create) → `mv`. Backs up to `<target>.secrets-bak` before the first merge.
+- **Properties separator parsing** (`_props_get`): key ends at the first `=`, `:`, or whitespace (after lstrip); handles `key=value`, `key = value`, `key:value`, `key value`; last definition wins.
+- **Security:** the write target comes from a committed file, so `_validate_external_target_path` locks it down — basename must be `gradle.properties`, must resolve inside `$HOME` (deepest-existing-ancestor resolved, symlink target/parent refused, `..` rejected). This blocks a malicious manifest from appending decrypted keys to `~/.gitconfig`/`~/.bashrc`. `_parse_secrets_files_manifest` rejects shell metacharacters/control chars in path and keys (path allows `[A-Za-z0-9/._~-]` only; keys allow `[A-Za-z0-9._-]` + space), mirrors the `.secrets-store` posture (no shell expansion, symlinked manifest skipped).
+- **Plaintext tradeoff (accepted, documented):** merged keys are permanent plaintext in the target; `secrets clear` does not remove them. Fine for the Clerk *publishable* keys this was built for; not for high-value secrets (use `secrets run` + `.env`).
+
 ## Deploy Configuration
 
 - Platform: NONE (distributed via `git clone` from GitHub)