An adversarial security review of the Phase 2 trust model found four real
bypasses (two remote-triggerable to in-process code execution). Root cause for
three: the set of bytes verification covered was smaller than the set that
determined execution. Fixes:
1. Bytecode-cache blind spot (CRITICAL). verify_dir excluded __pycache__/.pyc,
so a planted cache ran while escaping the hash map. verify_dir now flags any
bytecode as an unexpected file; the loader strips bytecode before verify and
imports under sys.dont_write_bytecode, so only verified source executes.
2. Unauthenticated verify-at-load bypass (CRITICAL). load_plugin_class imported
plugin.py with no gate, reachable via discover_available / an anonymous GET
/api/plugins. The verify+strip gate moved INTO load_plugin_class - the single
import choke point every path flows through - so an unsigned/tampered plugin
is never imported. discover_available skips a refused plugin instead of 500.
3. Ungated migration entrypoints (HIGH). downgrade_plugin and get_current_head
(ScriptDirectory imports version modules) ran plugin code with no check. All
alembic-invoking methods now pass through _verify_ok (strip + verify) first
and run under no-bytecode.
4. Revocation/content bypass (HIGH). The signed index bound a filename, not
content; adopt did not bind the delivered bytes to the resolved version, so
revoked bytes could be served under a live filename. The index now records a
per-artifact SHA-256; adopt verifies the on-disk digest and requires the
artifact's own signed manifest version to equal the resolved version.
Enforcement stays default-off; strip/no-bytecode run only under enforcement, so
the unsigned path is unchanged. 6 regression tests (planted bytecode, the
discover import path, downgrade gate, version-swap). 1054 pass, naming green.
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