Preserve Alpaca short direction through connection and position closure #118

Affected version: 0.1.2; public main 43fc66f. Environment: Python 3.12, offline provider transports.

Observed behavior: The adapter treats unsigned Alpaca snapshot quantities as positive regardless of the side.

Expected behavior and acceptance: An SDK-valid short snapshot must produce a negative portable position. Closing it through the public broker must buy to cover the absolute quantity, with unchanged cash and pending state on an invalid snapshot.

Verify a public API or feed workflow fails against the unchanged producing base and passes with the repair. Record exact revisions and commands, run the applicable full quality gates, and preserve failure atomicity. No live-money orders or release actions.

This focused issue owns one repair originally reported in #111 and proposed in #112. Retain the original contributor's attribution. The bundled report remains open until all five independent problems are substantively resolved.

AI assistance: Codex prepared this focused maintenance issue from the existing report.