feat: add delivery-verification — session-end quality gate

[YuhaoLin2005]

What

A Stop hook that mechanically verifies session completeness. Checks learning capture, disk space, and rationalization patterns. Hard blocks (exit 2) when complex tasks complete without learning capture.

Why

Claude Code sessions accumulate knowledge, but without mechanical enforcement, learning capture is aspirational — "I'll write it next session" becomes never. This hook enforces the habit: complex task → must touch learning libraries.

How It Works

Stop hook → check disk (<15GB → block) → count edits → check 5 learning lib mtimes → detect rationalization patterns → >=3 stale + complex task → exit 2

Integration

Module B of a composable quality pipeline. Works standalone. Complements:

• pre-task-calibration (feat: add pre-task-calibration — mechanical pre-action verification #1422): pre-action verification
• persona-review (feat: add persona-review — multi-persona adversarial review skill #1420): adversarial depth
• neural-gate: post-session behavioral verification (separate PR)

Evidence

Merged in ECC (226K stars) as delivery-gate #2378 after full maintainer review. 50+ session production use. The boundary between warn and block: can this be fixed retroactively?