con-duct ls --eval-filter: silent/misleading on malformed expressions

[asmacdo]

Summary

Two related UX gaps in --eval-filter. Both classify as "filter expression is malformed" and should behave the same way: emit a clear single-line warning and return no rows.

1. Type-mismatch is silent. The filter namespace receives exit_code as int, so exit_code == '0' compares int to str and never matches. The column displays "0" and -f json emits "0" as a string, so the failing pattern looks right. The result is zero rows, no warning, no hint.
2. NameError is misattributed. An undefined identifier in the expression raises NameError during eval, but the current handler blames the file: Failed to load file <_io.TextIOWrapper name='.duct/logs/..._info.json' mode='r' encoding='utf-8'>: name 'foo' is not defined. The JSON load succeeded; the filter eval is at fault. The message also leaks the Python _io.TextIOWrapper repr and repeats once per file.

Reproducer — type mismatch (silent)

cd "$(mktemp -d)"
duct -- echo one >/dev/null
duct --fail-time 0 -- bash -c 'exit 1'
con-duct ls                                         # 2 rows, EXIT_CODE shows "0" / "1"
con-duct ls --eval-filter "exit_code == '0'"        # 0 rows (silent)
con-duct ls --eval-filter "exit_code == 0"          # 1 row

Reproducer — NameError misattribution

cd "$(mktemp -d)"
duct -- true
con-duct ls --eval-filter "foo == 'bar'"
# [WARNING] con_duct.ls: Failed to load file <_io.TextIOWrapper ...>: name 'foo' is not defined

Proposed behavior

One warning per invocation (not per file), blaming the expression:

• Type-mismatch:

  [WARNING] --eval-filter: 'exit_code' is int, compared to str — expression will never match
  

• NameError:

  [WARNING] --eval-filter: name 'foo' is not defined
  

Implementation-shape: split the try/except in ls.py that today wraps both the JSON load and the filter eval. JSON errors stay file-scoped; eval errors are expression-scoped and emit once.

Low-risk prerequisite: the filter expression can be pre-analyzed once per invocation (not once per file) to detect literal-type mismatches against the known field types (exit_code: int, message: str, etc.).

Scope

Reproduces on v0.19.0 and current main. Longstanding, not a regression. Surfaced during pre-0.20.0 QE.