fix(config): resolve agent/command names from relative paths

[kitlangton]

The bug (#25713)

When opencode runs in any environment whose home or parent directory contains the segment /agent/ or /agents/ — most commonly a Docker container running as a user literally named agent (home /home/agent/) — every project agent gets mis-keyed. Instead of build, the key becomes .config/opencode/agents/build. Any code that later looks up an agent by its short name fails.

The reporter's environment:

file path: /home/agent/.config/opencode/agents/build.md
expected agent key: "build"
actual agent key:   ".config/opencode/agents/build"

Why it happens

configEntryNameFromPath in packages/opencode/src/config/entry-name.ts searches the absolute file path for any of these substrings, first-match-wins:

const patterns = ["/.opencode/agent/", "/.opencode/agents/", "/agent/", "/agents/"]

For /home/agent/.config/opencode/agents/build.md:

1. /.opencode/agent/ — not present (the path is .config/opencode/, not .opencode/). Skip.
2. /.opencode/agents/ — not present. Skip.
3. /agent/ — matches at position 5, inside /home/agent/. Wins.
4. /agents/ — never tried.

indexOf returns the leftmost occurrence, so the slice keeps everything from /home/agent/ onward, leaking .config/opencode/agents/ into the key.

A second, related failure surfaces in any path with /agents/ as a parent segment (e.g. /srv/agents/team/.config/opencode/agents/build.md): the first /agents/ wins over the real one further right, producing the key team/.config/opencode/agents/build.

Why fixing the helper alone is fragile

I considered the surface-level patches:

• lastIndexOf instead of indexOf — only fixes the second case. For /home/agent/... there's a single /agent/ occurrence, so lastIndexOf still picks position 5.
• Sort patterns longest-first + lastIndexOf — handles both reported failures, but silently changes behavior for nested layouts like .opencode/agents/agents/foo.md (today: key agents/foo; after: foo). The shift would invisibly break any user with that layout who references the agent by its old key from opencode.json. Narrow edge case, but a real one.

Both options also leave the root cause in place: the helper is trying to reverse-engineer "where does the entry's directory start?" from a flat absolute path, when the caller already knows exactly where it starts — every call site does Glob.scan({ cwd: dir, absolute: true }) and has dir right there.

The fix

Anchor the prefix match at the caller by passing path.relative(dir, item) to the helper. The relative path of a globbed agent file is — by definition of the glob {agent,agents}/**/*.md — always agent/... or agents/.... The helper now uses startsWith instead of indexOf-anywhere.

packages/opencode/src/config/entry-name.ts

```ts
function stripPrefix(relativePath: string, prefixes: string[]) {
const normalized = relativePath.replaceAll("\\", "/")
for (const prefix of prefixes) {
if (normalized.startsWith(prefix)) return normalized.slice(prefix.length)
}
}
```

packages/opencode/src/config/agent.ts (and command.ts)

```ts
const name = configEntryNameFromPath(path.relative(dir, item), ["agent/", "agents/"])
```

Patterns collapse from four to two because the .opencode/-prefixed variants are no longer needed — the relative path is already rooted at agent//agents/.

Why this is safe

• No behavior change for any existing user. path.relative(dir, item) always produces a path rooted at agent/ or agents/ (the glob enforces it), so the new prefix match yields exactly the same key as the old code did for paths the old code resolved correctly. The only inputs whose result changes are the ones that were already buggy.
• Bug class structurally eliminated. The new helper can no longer be tricked by a parent segment, because it never sees one. There is no "earlier occurrence" to match against — the input begins at the prefix.
• loadMode unaffected. It passes an empty prefix array and relies on the basename fallback, which still works.
• Symlinks safe. Glob.scan({ cwd: dir, absolute: true }) returns the scanned absolute path (rooted at dir), not the symlink target, so path.relative(dir, item) is always clean.
• Same fix lands for commands (Agent name resolution broken when username contains "agent" #25713 is filed for agents but command.ts has the identical bug shape).

Test plan

• New file packages/opencode/test/config/entry-name.test.ts:
  • Happy-path: agents/build.md, agent/build.md, nested agents/team/build.md, Windows backslashes, basename fallback.
  • Two Agent name resolution broken when username contains "agent" #25713 regression cases that simulate the exact caller flow (path.relative(dir, item) → helper), one for the username-agent case and one for the parent-agents/ case. Both fail against the unpatched code with the reporter's exact symptom (e.g. .config/opencode/agents/build instead of build).
• All 173 existing config tests still pass.
• bun run typecheck clean.

Fixes #25713.