mise tasks validate passes a file task whose #USAGE spec does not parse

[Guria]

mise 2026.9.14 macos-arm64 (same on 2026.9.12)

A file task with a malformed #USAGE spec validates as clean. mise run then runs it with its arguments dropped.

mkdir -p demo/mise-tasks && cd demo && touch mise.toml
printf '#!/usr/bin/env bash\n#USAGE arg "<x" {{{\necho hi\n' > mise-tasks/bad
chmod +x mise-tasks/bad
mise trust
mise tasks validate --errors-only; echo "exit=$?"

mise WARN  invalid usage spec in task file …/demo/mise-tasks/bad
  × Found child block instead of node name
   ╭─[…/demo/mise-tasks/bad:1:11]
 1 │ arg "<x" {{{
   ·           ─┬
   ·            ╰── not node name
   ╰────
  (… five more KDL diagnostics for the same line …)
✓ All N task(s) validated successfully
exit=0

flag "--v" default=true (a KDL bool written as true instead of #true) takes the same path.

Two things line up:

1. parse_task_script_usage_or_warn warns and falls back to an empty spec, so by the time validate_usage_spec calls parse_usage_spec_for_display the parse succeeds and no issue is recorded:
   https://github.com/jdx/mise/blob/v2026.9.14/src/task/mod.rs#L1172
2. Even when usage-parse-error is recorded, it is Severity::Warning, which --errors-only drops:
   https://github.com/jdx/mise/blob/v2026.9.14/src/cli/tasks/validate.rs#L454-L470

The fallback makes sense for task loading (one bad spec shouldn't break every task). For tasks validate I'd expect an error and a non-zero exit, since the spec is what validate is there to check. We currently grep the WARN text in CI to catch this, and that broke silently when #13312 reworded the message.

[jdx]

Thanks for the precise diagnosis — both points were right. Fixed in #13672: mise tasks validate now parses file-task #USAGE specs strictly (no empty-spec fallback) and reports usage-parse-error as an error, so --errors-only exits 1 with the KDL diagnostic. You should be able to drop the WARN-text grep once it's released.

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