fix(postgresql): fail PITR WAL inspection errors

[weicao]

Summary

• check pg_waldump before extracting a commit timestamp during PITR restore
• distinguish a tool failure from a successful WAL containing no transaction records
• stop before pulling later WALs when an archived segment cannot be inspected

Contract anchors

• docs/addon-continuous-backup-pitr-chain-integrity-guide.md, pit 4: continuous/PITR chains fail closed rather than silently crossing uncertain segments
• docs/addon-api/09b-backup-extensions.md: restore must clearly fail when required repository artifacts cannot be validated
• docs/addon-api/09c-restore-and-rebuild.md: PITR validation includes the actual continuous chain and restored result

TDD evidence

RED commit 294968c5a (Bash 3.2): 12 examples, 1 failure / 3 failed assertions. A simulated pg_waldump rc46 on required WAL002 was treated as an empty-transaction WAL; restore returned success, pulled WAL003, and reported the target reached.

GREEN commit 15b4f7338374d178b51a3344842c4d764ea4de4a:

• focused PITR restore ShellSpec on Bash 3.2: 12 examples, 0 failures
• full PostgreSQL ShellSpec on Bash 5.3: 280 examples, 0 failures
• ShellCheck error severity, Bash syntax, and diff check: clean
• Helm lint: 1 chart, 0 failures
• Helm render: 41 documents, 1,013,453 bytes

Scope

Source/static product change only. Runtime package, environment, execution, cleanup, and formal repeated-full acceptance remain tester-owned and are not claimed here.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (f4d6a90) to head (15b4f73).

Files with missing lines	Patch %	Lines
...ns/postgresql/scripts-ut-spec/pitr_restore_spec.sh	0.00%	9 Missing ⚠️

Additional details and impacted files

@@                             Coverage Diff                             @@
##           easton/pg-pitr-restore-commit-time-failfast   #3397   +/-   ##
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  Coverage                                         0.00%   0.00%           
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  Lines                                            28329   28338    +9     
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- Misses                                           28329   28338    +9     

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