Policy engine and CLI built around prefix_rule(pattern=[...], decision?, match?, not_match?).
This release covers the prefix-rule subset of the execpolicy language; a richer language will follow.
Tokens are matched in order; any pattern element may be a list to denote alternatives. decision defaults to allow; valid values: allow, prompt, forbidden.
match / not_match supply example invocations that are validated at load time (think of them as unit tests); examples can be token arrays or strings (strings are tokenized with shlex).
The CLI always prints the JSON serialization of the evaluation result.
The legacy rule matcher lives in codex-execpolicy-legacy.

Policy shapes

Prefix rules use Starlark syntax:

prefix_rule(
    pattern = ["cmd", ["alt1", "alt2"]], # ordered tokens; list entries denote alternatives
    decision = "prompt",                 # allow | prompt | forbidden; defaults to allow
    match = [["cmd", "alt1"], "cmd alt2"],           # examples that must match this rule
    not_match = [["cmd", "oops"], "cmd alt3"],       # examples that must not match this rule
)

CLI

Provide one or more policy files (for example src/default.codexpolicy) to check a command:

cargo run -p codex-execpolicy -- check --policy path/to/policy.codexpolicy git status

Pass multiple --policy flags to merge rules, evaluated in the order provided:

cargo run -p codex-execpolicy -- check --policy base.codexpolicy --policy overrides.codexpolicy git status

Output is JSON by default; pass --pretty for pretty-printed JSON
Example outcomes:
- Match: {"match": { ... "decision": "allow" ... }}
- No match: "noMatch"

Response shapes

Match:

{
  "match": {
    "decision": "allow|prompt|forbidden",
    "matchedRules": [
      {
        "prefixRuleMatch": {
          "matchedPrefix": ["<token>", "..."],
          "decision": "allow|prompt|forbidden"
        }
      }
    ]
  }
}

No match:

"noMatch"

matchedRules lists every rule whose prefix matched the command; matchedPrefix is the exact prefix that matched.
The effective decision is the strictest severity across all matches (forbidden > prompt > allow).