#206 swamp extension outdated crashes on empty repo (Stream ended...)

Summary

swamp extension outdated exits with a fatal error when run in a repository that has no installed extensions. Both the TTY/log form and --json form fail.

Reproduce

mkdir /tmp/repro-outdated && cd /tmp/repro-outdated
swamp repo init
swamp extension outdated --log --no-color
# → [FTL] error: Error: Stream ended without a completed or error event
# → exit 1

swamp extension outdated --json
# → {"error": "Stream ended without a completed or error event", "stack": "..."}
# → exit 1

Expected

Empty installed-extension list should produce an empty result and exit 0 — same shape as swamp extension outdated with extensions installed but all up-to-date:

extension·outdated: All extensions are up to date.

{ "extensions": [], "hasUpdateAvailable": false }

Stack trace

[FTL] error: Error: Stream ended without a completed or error event
    at result (file:///.../libswamp/stream.ts:77:9)
    at async Command.<anonymous> (file:///.../cli/commands/extension_outdated.ts:133:23)

Workaround

Pull at least one extension before running outdated (swamp extension pull @swamp/gcp/workstations); the non-empty path works correctly.

Version

swamp 20260501.150516.0-sha.acc85d5a (current stable).

Context

Discovered while writing the extension-management.md reference page (swamp-club #203). Blocks documenting the empty-repo outcome of outdated cleanly, so the doc will use a populated-repo example instead.