fix(postgresql): make PITR restore_command replayable and timestamp comparison numeric

[weicao]

Problem

Deep-review finding 三.20 (issue #3071):

1. restore_command consumed segments with mv: PostgreSQL re-requests earlier WAL segments through restore_command whenever recovery restarts mid-way (pod eviction, OOM, node restart — routine on Kubernetes). With mv, those segments are gone from the staging dir and the restore can never complete — the PITR attempt is burned. The .history branch already used cp, conceding the point.
2. Lexicographic timestamp comparison in fetch-wal-log's stop condition ([[ $ts > $rt ]]): both operands are epoch seconds of currently-equal width, so it is accidentally correct today — a latent trap.

Changes

• restore_command='cp ${PITR_DIR}/%f %p' for all files (PostgreSQL's own documented example shape). Disk boundary: fetch-wal-log stages the whole window up front, so the peak is already paid; cp adds only transient pg_wal duplication bounded by recovery checkpoint recycling.
• -gt for the epoch comparison.
• New spec (3 examples) that executes the same concatenation the ActionSet builds (set -e + common-scripts + fetch-wal-log + pitr-restore): pins the cp restore_command, the staging + idempotent-retry behavior, and the timestamp fix via a 9-digit/10-digit epoch pair that discriminates lexicographic from numeric comparison.

Evidence boundary

Static + concatenated-form shellspec (suite 23/23 locally, shellcheck clean at CI severity). The mid-recovery-restart replay scenario is not runtime-reproduced; it will be covered in the draft-batch integration round (T3 PITR window) and/or the #postgresql team's kubeblocks-tests negative-path cases (task #29 alignment).

Opened as draft per the batch process (tests pass → ready). Will be added to integration/pg-review-batch.

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (35e0ded) to head (f215a27).

Files with missing lines	Patch %	Lines
...ns/postgresql/scripts-ut-spec/pitr_restore_spec.sh	0.00%	67 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3072   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        144     145    +1     
  Lines      23013   23080   +67     
=====================================
- Misses     23013   23080   +67     

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