Fix caller transaction graph handoff

[Haider Z (haiderz07)]

Summary

• track the top-level PostgreSQL transaction that owns caller-mode df.start() graph rows
• probe graph visibility and pg_xact_status() with bounded single-shot activities plus deterministic durable backoff
• retry transient database failures, distinguish whole-transaction aborts from committed savepoint rollbacks, and compact long waits with continue_as_new
• preserve historical replay by retaining the original activity name and raw instance-ID input for orchestration inputs without an origin xid

Problem

df.start() persists df.instances / df.nodes in the caller transaction but commits the duroxide start separately. The graph loader previously stopped waiting after five seconds. A legal transaction held for eight seconds then committed with the control-plane row still pending, no SQL effect, and the engine execution terminally Failed with Instance <id> not found after 5s.

Synthetic reproducer:

BEGIN;
SELECT df.start('INSERT INTO effects VALUES (''{sys_instance_id}'')');
SELECT pg_sleep(8);
COMMIT;

The new regression also terminates a lock-blocked management backend and holds the lock long enough for the next probe to time out, proving both transient error paths retry and the effect still occurs exactly once.

Compatibility

No extension schema, ABI, or persisted df data changes. Historical FunctionInput payloads default origin_xid to None and schedule pg_durable::activity::load-function-graph with the same raw input bytes and operation order. New starts alone use the versioned transaction-aware probe activity. Upgrade B1 passed against every supported v0.2.2-v0.2.6 schema on PostgreSQL 17 and 18.

Validation

• cargo fmt -p pg_durable -- --check
• PG17 + PG18 cargo build and cargo clippy -- -D warnings
• PG17 + PG18 cargo pgrx test: 333 passed, 0 failed, 16 ignored each
• PG17 + PG18 full local E2E: 56 passed, 0 failed each
• new transaction regression: 3 consecutive PG17 runs, plus PG18
• PG17 + PG18 upgrade tests: 86 passed each
• PG17 + PG18 pg_regress: 6 passed each
• PG17 + PG18 shutdown and extension-epoch race regressions
• synthetic immediate-stop and worker-kill matrices across SQL, JOIN, RACE, loop, timer, signal, and cancellation

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[waldemort-auto]

Review verdict: changes requested

Three independent specialist passes reviewed this head for PostgreSQL transaction semantics, durable replay compatibility, and Rust reliability. The transaction-handoff direction is sound, but three production correctness/liveness issues and two regression-test gaps should be resolved before merge. CI remains the source of test results.

[waldemort-auto]

High — committed is not yet guaranteed to be snapshot-visible. PostgreSQL can record the transaction as committed before ProcArrayEndTransaction removes it from the running set used by a fresh snapshot. In that window, the immediate find_visible_instance() re-read can still return None, causing a valid committed graph to be permanently classified as CommittedMissing. After observing committed, first check pg_visible_in_snapshot(origin_xid, pg_current_snapshot()); if it is false, return Retry. Declare CommittedMissing only after the xid is snapshot-visible and the graph remains absent. Please add focused coverage for this handoff boundary.

[waldemort-auto]

High — the two-second deadline can livelock a valid graph load. This timeout covers role validation, fetching up to MAX_GRAPH_NODES (10,000), constructing the graph, and serialization. A valid graph that consistently needs more than two seconds returns Retry forever; durable backoff and continue_as_new bound history but never let the workflow execute or fail. Keep the short deadline on visibility/transaction-status probes, but give graph loading a separate policy: a suitable statement/lock timeout plus a bounded retry budget and terminal error.

[waldemort-auto]

High — permanent database errors retry forever. Errors from visibility checks, pg_xact_status(), and the Retryable graph-load branch all become Retry without a cumulative ceiling. Conditions such as 42501 (insufficient_privilege), 42883 (undefined_function), 42P01 (undefined_table), and schema/decode incompatibilities cannot recover through polling, so the orchestration remains running indefinitely with misleading transaction-wait logs. Allowlist genuinely transient SQLSTATEs and connection failures, propagate all other errors as terminal with their SQLSTATE/message, and consider a bounded budget even for transient failures.

[waldemort-auto]

Medium — this regression does not prove the timeout path executed. The test terminates one lock-blocked management backend and waits three seconds, but it never proves that a second probe started and reached its two-second timeout before COMMIT; that probe can simply resume after the lock is released and the test still passes. The PID filter can also select an unrelated management query. Identify the backend by query/locked relation and instance where possible, then assert an observable second retry or timeout outcome before releasing the lock.

[waldemort-auto]

Low — NULL diagnostic output bypasses the rollback assertion. In PL/pgSQL, when the status is failed and engine_output is NULL, false OR NULL evaluates to NULL, and IF NULL THEN does not enter the failure branch. Add engine_output IS NULL OR ... to both the whole-rollback and savepoint-rollback checks so missing diagnostics fail the test.