test(ha-entity-snapshots): RED tests for load_snapshot restore contract (task 5.1)

Extends persist_load_snapshot's public signature with an
out_entities_restored bool*, per design.md's documented contract. The
static load_snapshot function -- the real restore logic -- is completely
untouched (still today's watermark-only implementation, byte-identical
to before this task); only a thin wrapper was added that naively maps
*out_entities_restored = (rc==0), deliberately scaffolding so the 3 new
RED tests fail for genuine reasons rather than accidentally passing.
ha_handle_snapshot_chunk's sole call site gets a mechanical
declare-and-pass update -- confirmed inert, never reads the new
out-param (task 6.1's job).

Three tests against persist_load_snapshot directly (unlike prior tasks'
tests, which deliberately stayed on the raw-byte-parsing side to avoid
this exact function): restore-before-advance (fails at the job-lookup
assertion -- nothing is ever restored today), corrupted-entity-leaves-
position-unchanged (fails at rc!=0 -- today's code ignores the corrupted
section entirely, since load_snapshot never reads past the legacy
header), legacy-file-reports-position-only (fails at entities_restored==
false -- the naive wrapper claims restoration for every rc==0 case,
including legacy files).

This is the exact function/call site that caused task 2.2's rejection
(a live position-advances-before-restore-validates hazard). Independent
review verified load_snapshot's body is byte-identical to commit
d52eb94, the wrapper does nothing beyond the naive mapping, and ha.c's
change never reads the new out-param anywhere -- no repeat of that
mistake here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JDYFbrgyDHbvNYcxApKhrX

.kiro/specs/ha-entity-snapshots/tasks.md

@@ -70,7 +70,7 @@
   - _Requirements: 3.1, 3.2, 3.3_
 
 - [ ] 5. Core: entity restoration on load
-- [ ] 5.1 RED: restore-before-advance, failure-safety, and legacy-format tests
+- [x] 5.1 RED: restore-before-advance, failure-safety, and legacy-format tests
   - Assert loading a checkpoint with N jobs + M queues restores all of them before the member's
     position advances
   - Assert a deliberately corrupted entity record causes the load to fail with the member's
@@ -133,3 +133,4 @@
 - (3.2) Pre-existing ASan leak in the test fixture itself (`snapent_make` -> `makeInstance`/`makeJob`/`makeQueue`/`xkvmgr_add`, ~18KB/113 allocations), unrelated to any production code -- present since task 1.1, masked by the project's standing `ASAN_OPTIONS=detect_leaks=0` convention for this suite. Not blocking any task; worth a dedicated fixture-teardown cleanup pass if this test file keeps growing.
 - (4.1) `snapshot_inflight_lsn[peer_idx]` clears to 0 BEFORE `snapshot_inflight[peer_idx]` clears to 0 in every path (completion + all 3 failure sites in `ha_snapshot_send_dispatch`). Task 4.3's `rotate_snapshots` consultation must therefore treat `snapshot_inflight_lsn[i] != 0` as the "protected" signal directly (checkpoint LSNs are never 0), not "check flag==1 first, then trust LSN" -- there's a narrow window where the flag is still 1 but the LSN has already cleared.
 - (execution note, after 4.1) Remaining tasks split by risk given a mid-session spend-limit hit: low-risk/small/isolated tasks (4.2, 4.3, 7.1, 8.1) executed directly in the main context with self-review (build + test + boundary/TBD/secrets grep), no subagent dispatch. High-risk tasks (5.1/5.2 `load_snapshot` restore -- the exact function that caused task 2.2's rejection; 6.1 wiring into the live `ha_handle_snapshot_chunk` production path) keep the full implementer + independent-reviewer subagent cycle, since that adversarial review already caught a real live-hazard bug once this spec (task 2.2) and the remaining risk is concentrated there, not spread evenly.
+- (5.1) `persist_load_snapshot`'s wrapper currently maps `*out_entities_restored = (rc==0)` -- a deliberately naive stopgap so the 3 RED tests fail for the right reasons. `load_snapshot`'s real body is completely untouched (still watermark-only, byte-identical to before this task). Task 5.2 must replace the wrapper's naive mapping wholesale with real format-detection + restore-then-gate-position logic; it owns turning `load_snapshot` from a no-op-on-entities function into the real restore path.