fix(agent): is_verify_command_inert misses mise's "unknown command" output — INERT build-gating warning never fires

[srbhsrkr]

Component

Agent (Python runtime)

Describe the bug

is_verify_command_inert() (agent/src/post_hooks.py:77-99) fails to recognise mise's actual "task does not exist" phrasing, so a repository with no mise.toml at all is never classified as inert.

The most damaging consequence is not the wrong build_passed/lint_passed value — it is that the operator-facing warning at agent/src/repo.py:517-526 never fires:

if not config.build_command and is_verify_command_inert(result.returncode, result.stderr):
    build_gate_inert = True
    notes.append(
        "⚠️ Build-regression gating is INERT: no runnable `mise run build` task ..."
    )

Because the detector returns False, that note is never appended. A repo onboarded with no pipeline.buildCommand and no mise.toml therefore gets build-regression gating silently disabled with no warning to anyone — precisely the failure mode the warning exists to prevent.

Expected behavior

mise run build / mise run lint in a repo with no mise.toml should be detected as inert, so that:

1. build_gate_inert / lint-inert is set,
2. the "⚠️ Build-regression gating is INERT" note is appended and surfaced on the PR, and
3. build_passed / lint_passed reflect inert-treated-as-passing rather than a bogus red.

Current behavior

The detector returns False, no inert warning is emitted, and lint_passed is persisted as false on every task against such a repo.

Reproduction steps

In any checkout with no mise.toml (e.g. a clone of aws-samples/sample-semantic-layer-structured):

$ mise run lint; echo "EXIT=$?"
mise ERROR unknown command: lint

Did you mean:
  mise install-into
  mise plugin-list
mise ERROR Version: 2026.8.4 macos-arm64
EXIT=1

Then feed that verbatim to the detector:

$ python3 -c "
import sys; sys.path.insert(0,'agent/src')
from post_hooks import is_verify_command_inert
print(is_verify_command_inert(1, 'mise ERROR unknown command: lint'))"
False

The heuristics check exit 127, "no tasks defined", "no task named", "mise" + "not found", and "command not found". Real mise emits unknown command with exit 1, matching none of them.

Observed in practice on task 01KZS7NFB480DGF2A6FZ5N3CZD and 01KZS86KNZPVK8FZXX757ADZ8S (both lint_passed=false, no inert note on the PR).

Possible solution

Add mise's real phrasing to the heuristic list in is_verify_command_inert:

or "unknown command" in s

Worth reviewing the full set of mise task-missing messages across versions rather than adding one string, and adding a regression test that feeds the verbatim stderr above. Note the mise version string is included in that stderr, so a test fixture should not match on version.

Related: the same detector is used for the post-agent gate in agent/src/post_hooks.py and for the lint inert path, so build and lint inert handling are both affected by the single missed match.

[srbhsrkr]

Found alongside #750 and #751 in the same end-to-end validation session (onboarding a non-mise Python repo and exercising build-regression gating). #750 is the closest sibling: both are cases where the build-verify path fails to recognise "this command verified nothing" and takes a worse branch than the inert path that already exists.