fix: while/do-while loop condition reads stale iteration-0 step output (#2662)

* fix: while/do-while loop condition reads stale iteration-0 step output

After executing namespaced loop body steps, copy each iteration's
results back to the original unprefixed step key so that
evaluate_condition() sees the latest values instead of stale
iteration-0 data.

Fixes #2592

* address review: cross-platform tests, preserve iteration-0 history

- Rewrite shell scripts in tests to use Python via script files
  instead of POSIX syntax, so they pass on Windows CI.
- Snapshot iteration-0 nested-step results under a namespaced key
  (parent:child:0) before the first copy-back overwrite, preserving
  complete per-iteration history for debugging.

* address review: skip copy-back on paused/failed iterations

Move the status check before the copy-back so that partial results
from paused or failed nested steps (e.g., a gate awaiting input)
do not overwrite the unprefixed key. This preserves correct resume
behavior.

* address review: quote paths in test shell commands

Quote both the Python executable and script file paths in the
run: commands to handle spaces in paths on Windows.

* address review: execute loop body with original IDs

Instead of namespacing step IDs for execution and copying results
back, execute the loop body with original (unprefixed) step IDs so
results naturally land at the right keys.  Snapshot previous
iteration results to namespaced keys (parent:child:N) for history
only.

This fixes multi-step loop bodies where step B references step A's
output within the same iteration — previously step B would see
stale data until the copy-back ran after the entire iteration.

* address review: namespaced execution with per-step copy-back

Revert to namespaced step IDs for execution (preserving unique
log entries and state keys per iteration) but copy each step's
result back to the unprefixed key immediately after it completes.

This preserves backward compatibility (same namespaced key format,
same log IDs) while fixing both the condition evaluation bug and
inter-step references within multi-step loop bodies.

* address review: alias after status check, add multi-step body test

- Move per-step aliasing below the PAUSED/FAILED/ABORTED status
  check so partial results from incomplete steps are not aliased
  back to the unprefixed key.
- Add test_while_loop_multi_step_body_inter_step_refs to exercise
  a multi-step loop body where step B reads step A's output within
  the same iteration, verifying per-step aliasing works correctly.

Addresses feedback from @doquanghuy (items 2 & 4) and Copilot
review on commit 9d0a222.

* address review: stable fallback IDs, expression-based inter-step test

- Use enumerate() for stable fallback IDs when loop body steps lack
  an explicit id (step-0, step-1, etc. instead of always step-0).
- Rewrite multi-step body test so step B uses expression
  substitution ({{ steps.step-a.output.stdout }}) instead of
  reading the counter file directly, making it a true regression
  test for per-step aliasing.