Hook execution: double callback on throw + swallowed hook-load errors

[dalberola]

Two issues in the hooks pipeline (agent-reported; [needs repro] but grounded in the code).

1. try/catch can invoke the callback twice

packages/dredd/lib/TransactionRunner.js:361-405 (runHookWithData). The try/catch wraps the entire callback chain, so an error thrown after this.runHook(...) (e.g. inside runHookCallback()) is caught and runHookCallback() is called again. The code itself comments that this is "very problematic."

Fix: wrap only the this.runHook() call, or guard with a once-flag so the callback fires exactly once.

2. Hook-load errors swallowed

packages/dredd/lib/addHooks.js:23-34 (loadHookFile). An invalid hook file only emits logger.warn and execution continues without the hooks the user expected — unlike the fail-fast hookHandlerError pattern used elsewhere.

Decision needed: propagate the error (fail fast) vs. keep warn-and-continue. If kept, document it as intentional.

Tasks

• Narrow the try/catch in runHookWithData and/or add a once-guard on the callback.
• Decide and implement fail-fast vs. documented warn-and-continue for hook-load errors.
• Tests covering a throwing hook and an unloadable hook file.

[dalberola]

PR #16 implements both items. Tech-lead call: fail fast on hook-load errors (silent skip = falsely-passing run). Verified no test/fixture pinned warn-and-continue; added a load-failure fixture + test. Double-callback guarded with a once-flag. 179 unit tests pass. Behavior change (broken hook file now fails the run) noted for release notes.