fix(connectors): defer postgres source progress until ack

[rohankumardubey]

Which issue does this PR address?

Closes #3635

Rationale

The PostgreSQL source advanced tracking offsets, deleted or marked rows, and consumed CDC changes before Iggy confirmed delivery. A failed send could therefore permanently skip source records.

What changed?

PostgreSQL polling now stages cursor updates and row operations until the runtime reports a successful batch acknowledgment. NACK discards the staged work, while ACK commits the state and performs the pending delete or mark operations.

CDC now peeks logical-slot changes and advances the slot only after acknowledgment. A deterministic regression test stops Iggy during delivery and verifies that the PostgreSQL rows are redelivered after restart.

Local Execution

• Passed cargo fmt --all -- --check
• Passed cargo clippy -p iggy_connector_postgres_source -p integration --all-features --all-targets -- -D warnings
• Passed all 70 PostgreSQL source unit tests
• Passed all 7 PostgreSQL polling integration tests
• Passed both PostgreSQL CDC integration tests
• Passed the deterministic kill-server regression test
• Passed git diff --check

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer

See CONTRIBUTING.md for details.

[codecov]

Codecov Report

❌ Patch coverage is 80.88235% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.69%. Comparing base (a65f177) to head (9ed427d).

Files with missing lines	Patch %	Lines
core/connectors/sources/postgres_source/src/lib.rs	80.88%	19 Missing and 7 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3957       +/-   ##
=============================================
- Coverage     83.93%   57.69%   -26.24%     
  Complexity     1358     1358               
=============================================
  Files          1213     1212        -1     
  Lines        168441   139746    -28695     
  Branches     135999   107313    -28686     
=============================================
- Hits         141373    80622    -60751     
- Misses        23389    55625    +32236     
+ Partials       3679     3499      -180     

Components	Coverage Δ
Rust Core	50.16% <80.88%> (-34.56%)	⬇️
Java SDK	66.67% <ø> (ø)
C# SDK	76.52% <ø> (ø)
Python SDK	90.13% <ø> (ø)
PHP SDK	84.48% <ø> (ø)
Node SDK	95.81% <ø> (-0.10%)	⬇️
Go SDK	68.37% <ø> (+0.07%)	⬆️

Files with missing lines	Coverage Δ
core/connectors/sources/postgres_source/src/lib.rs	73.79% <80.88%> (+0.47%)	⬆️

... and 405 files with indirect coverage changes

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[rohankumardubey]

/ready

[rohankumardubey]

/request-review @hubcio

[hubcio]

a few things without diff lines to hang them on:

• .claude/skills/connector-source/SKILL.md still teaches the pre-ack pattern this pr removes (the "matches poll_tables" snippet writes cursors during poll, "always return state in every ProducedMessages" no longer holds for empty polls, and state-serialization failure is now a hard poll error, lib.rs:288-296) and doesn't mention on_batch_result at all - needs an update to the new contract.
• mark_or_delete_processed_rows maps db errors to Error::InvalidRecord (lib.rs:732, :751) - misleading now that these errors surface through the ack path; Error::Connection like advance_replication_slot uses would fit better.
• README.md:15 still promises offset tracking "avoid duplicates" - at-least-once redelivery means duplicates are possible; and README.md:57 documents the poll_interval default as 1s while the code fallback is 10s (lib.rs:180).