fix(opencode): support custom data dir and DB prefix

[ozymandiashh]

Summary

Fixes #617 by teaching the OpenCode provider how to read renamed or forked OpenCode-compatible installs without changing the default OpenCode behavior.

Root cause

The provider always derived the OpenCode data root as:

$XDG_DATA_HOME/opencode
~/.local/share/opencode

and only discovered SQLite files matching:

opencode*.db

That works for upstream OpenCode, but forks such as MiMoCode can keep the same storage schema while writing to a different data directory and DB prefix, for example:

~/.local/share/mimocode/mimicode.db

In that case CodeBurn silently reported zero OpenCode usage because neither the directory nor the DB filename matched the hard-coded defaults.

What changed

• Added OPENCODE_DATA_DIR as an exact OpenCode-compatible data directory override.
• Added OPENCODE_DB_PREFIX for SQLite discovery, so forks can expose files such as mimocode.db or mimocode-channel.db.
• Kept default discovery unchanged when the new env vars are unset:
  • $XDG_DATA_HOME/opencode
  • ~/.local/share/opencode
  • opencode*.db
• Applied the same custom data root to file-based OpenCode storage under storage/.
• Added the new OpenCode env vars to the session cache fingerprint so changing the directory or DB prefix does not serve stale cached results.
• Added the new vars to test env isolation.
• Documented both vars in the provider docs and README.

Behavior

# Default upstream OpenCode behavior stays the same
codeburn report --provider opencode

# Renamed/forked install with a different root and DB prefix
OPENCODE_DATA_DIR="$HOME/.local/share/mimocode" \
OPENCODE_DB_PREFIX="mimocode" \
codeburn report --provider opencode

OPENCODE_DATA_DIR is treated as the exact data directory. CodeBurn does not append an opencode suffix to it.

OPENCODE_DB_PREFIX only affects SQLite discovery. File-based storage is still discovered from <OPENCODE_DATA_DIR>/storage/.

One edge case is handled intentionally: an empty OPENCODE_DB_PREFIX falls back to the default opencode prefix. Without that guard, an empty prefix would match every .db file in the data directory.

Compatibility and safety

• Existing OpenCode users keep the same default discovery path and DB prefix.
• Existing createOpenCodeProvider(tmpDir) test fixtures keep working because that explicit test seam still appends opencode.
• OpenCode cache entries may rebuild once after upgrade because the provider env fingerprint now includes the new variables. Other providers are not affected.
• No public API exports were added.

Testing

Passed:

./node_modules/.bin/vitest run tests/providers/opencode.test.ts tests/providers/opencode-file.test.ts
# 56 passed

./node_modules/.bin/vitest run tests/session-cache.test.ts tests/provider-registry.test.ts
# 68 passed

./node_modules/.bin/tsc --noEmit
npm run build
git diff --check

env -u PYTHONPATH -u VIRTUAL_ENV -u PYTHONHOME semgrep --config .semgrep/rules/no-bracket-assign-hot-paths.yml --strict --json src/providers/ src/parser.ts
# 0 findings

Also ran a held-out smoke test that creates both a fork-style mimocode/mimicode.db and a default opencode/opencode.db store, then verifies both discovery modes. It printed:

PASS env override smoke

Full suite note:

./node_modules/.bin/vitest run

The full suite still has unrelated failures in tests/cli-proxy-path.test.ts and tests/cli-status-menubar.test.ts. I reproduced the same failure classes on main before this change, so they are not introduced by this PR.