feat(rule): enforce compound POSIX commands

[ronheichman]

Summary

• enforce already-matching shell rules against eligible static commands inside compound POSIX input
• keep detection on the complete command list and preserve the rule's original CEL result
• keep same-script function bodies, interpreter scripts, unsafe pipelines or enclosing redirects, malformed input, and compound PowerShell/CMD input detection-only
• apply the same eligibility checks to sequence rules and invalidate persisted verdict masks from the previous behavior

Detection runs first against the complete event. Candidate evaluation can only suppress enforcement when no independently safe command satisfies the same rule; it cannot create a finding or turn a non-match into a deny. POSIX branch and loop commands count as requested code without attempting to predict runtime control flow. Function bodies remain detection-only because shell state can replace or remove a definition before it is called.

Candidate programs and projections are built only for enabled enforcement rules that reference shell_commands, keeping monitor-only startup and evaluation close to the existing cost.

There are no schema, wire-format, or dependency changes.

Why

An enforce-enabled rule can detect cat .env inside echo ready; cat .env, but the existing event-wide safety check prevents a deny. Independent candidate eligibility closes that gap without changing detection semantics or trusting inferred function state.

Verification

• go test ./...
• go test -race ./...
• go vet ./...
• golangci-lint v2.12.2 run
• golangci-lint v2.12.2 fmt --diff
• govulncheck v1.6.0 ./...
• go generate ./rules with no generated diff
• go mod tidy with no module diff
• FuzzAnalyzeShellCommands for 30 seconds
• CGO-free Darwin, Linux amd64, and Windows amd64 builds