[EPIC] action.yml hardening audit (F2 round)

gh issue create --title "[EPIC] action.yml hardening audit (F2 round)" --label "epic,audit" --body "## EPIC: action.yml hardening audit (F2 round)

Source: F2 audit round, 2026-09-03. This EPIC aggregates the 6 findings from the action.yml audit (2 HIGH, 2 MEDIUM, 2 LOW).

action.yml is the public contract of the action; HIGH-2 (missing outputs:) breaks the schema and the data-flow contract with downstream steps.

### HIGH

- [ ] #164 concurrency_lock description documents the v2.8.0 inline-lftp shape (existing; F2 added detail)
- [ ] #197 action.yml H2 — declare outputs (log_file etc.); entrypoint.sh writes to GITHUB_OUTPUT

### MEDIUM

- [ ] #198 action.yml M1 — concurrency_lock_poll_interval description doesn't document '> 0' restriction
- [ ] #199 action.yml M2 — top-level description says 'delete remote folder before' which is misleading

### LOW

- [ ] #200 action.yml L1 — mirror_verbose description promises '(0-3)' but validation only checks >= 0
- [ ] #201 action.yml L2 — server description is too terse for an input with complex URL shape

## Suggested resolution order

1. Land H2 (outputs:) in the same v2.11.3 as lib.sh CRIT-1 — declaring outputs is a prerequisite for the retry-classifier work that will write a 'last_error' output.
2. Land the documentation drift fix for #164 together with the entrypoint.sh C1 fix.
3. Batch the MEDIUMs + LOWs into a docs-cleanup release.

## Source

F2 audit 2026-09-03 (action.yml audit). Reporter: subagent-pekodbj7."

Review action.yml and the child issues #164 and #197-#201 first; entrypoint.sh and lib.sh are also named in the proposed resolution. Confirm each audit finding, then use the child issues to track completion of the output declaration and documentation fixes. Done means all six findings are resolved and the stated release-order dependencies are addressed.

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