fix(search): search installed skills across all agents

[mrrobertkent]

Problem

skilld search reports nothing indexed when a project has more than one agent directory.

$ skilld search "config file" -p unlighthouse
▲  No docs indexed for "unlighthouse". Run `skilld add unlighthouse` first.

$ skilld list
unlighthouse-skilld  0.18.0  harlan-zw/unlighthouse/tree/v0.18.0/docs  today

readProjectLock resolved the lockfile through detectTargetAgent():

const agent = detectTargetAgent()
if (!agent)
  return null
return readLock(`${cwd}/${agents[agent].skillsDir}`)

detectTargetAgent() checks agent env vars first, then scans the project and returns null when several match:

return projectMatches.length === 1 ? projectMatches[0]! : null

A project with .claude/ and .agents/ produces null, so listLockPackages() returns [] and search bails. It only worked when run from inside an agent, where the env var short-circuits detection. From an ordinary terminal it always failed.

Change

Indexes are keyed by package and version:

export function getPackageDbPath(name: string, version: string): string {
  return join(getReferencesDir(name, version), 'search.db')
}

Nothing about them is agent-specific, so scoping the lockfile to one agent only hides skills the project has. iterateSkills in the same module already reads every agent by default, which is why skilld list works:

const agentTypes = opts.agents ?? (Object.keys(agents) as AgentType[])

Search now does the same, merged through the existing mergeLocks, which prefers the most recent syncedAt per skill. A skill installed for two agents resolves to one index, so the union deduplicates by construction.

--agents narrows when that is wanted:

skilld search "routing"
skilld search "routing" --agents claude-code
skilld search "routing" --agents claude-code,codex

Named --agents because the root command owns -a/--agent as an enum and citty validates parent args.

readProjectLock moves from commands/search-helpers.ts to core/skills.ts, next to the equivalent skill-directory resolution.

Coverage

test/unit/project-lock.test.ts covers no lockfile, a single agent, merging across agents, deduplication by newest syncedAt, narrowing by agent, an agent with no lockfile, and a shared .skills directory taking precedence.

Docs

README documents --agents in the command table, adds an example, and notes that search spans every agent by default.