Malformed plan files crash the CLI instead of returning validation errors

[Calmingstorm]

Failure scenario

Run odin validate or the legacy plan CLI's run command against syntactically valid YAML/JSON with a wrong structure, for example:

name: bad
steps: not-a-list

or a step with params: [], missing id, nonnumeric timeout, or a top-level YAML scalar.

load_plan() performs mapping/list operations and numeric casts without shape validation, producing uncaught AttributeError, TypeError, KeyError, or ValueError. Both CLI paths call it outside any error handler, so the command prints a Python traceback and exits 1 rather than reporting the invalid fields and returning the documented validation exit code 2. A plan with params: [] can even load successfully and then fail later in parameter resolution.

Sites

• src/odin/plan_loader.py:29-33 passes arbitrary decoded YAML/JSON directly to _from_dict().
• src/odin/plan_loader.py:40-68 assumes mapping/list/step shapes and coerces values without structured errors.
• src/odin/cli.py:57-70 calls load_plan() outside the PlanValidationError handling boundary.

Expected result

Validate the complete decoded plan schema before constructing dataclasses and convert all user-input failures into clear field-specific validation messages with exit code 2 and no traceback.

[Calmingstorm]

The standalone plan engine was removed in v4.7.0 (PR #367), so this no longer applies.