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).

[hubcio]

@rohankumardubey please write
/ready
when PR is ready for review. at any top level comment, in the beginning of any line. this will let know maintainers that something is ready for review by flipping gh labels.

[rohankumardubey]

/ready