Add API for source metadata snapshots

[KyleAMathews]

Plug to create a comprehensive snapshot of the source's metadata for debugging purposes.

Returns a JSON object containing:

Global Metadata

• database: Current PostgreSQL snapshot information
  • xmin: Oldest visible transaction ID
  • xmax: Next transaction ID to be assigned
  • xip_list: List of in-progress transaction IDs
  • lsn: Current WAL log sequence number (as string)
• status: Service connection status
• shape_count: Total number of active shapes

Per-Shape Metadata (in shapes array)

• handle: Unique shape identifier
• definition: Shape definition including table, where clause, columns
• status: Shape status (snapshot_started, snapshot_completed)
• latest_offset: Current log offset for this shape
• pg_snapshot: PostgreSQL snapshot at shape creation time (if available)

{
  "database": {
    "xmin": 12345,
    "xmax": 12347,
    "xip_list": [12346],
    "lsn": "100"
  },
  "status": {
    "connection": "up",
    "shape": "up"
  },
  "shape_count": 2,
  "shapes": [
    {
      "handle": "items-1234567890",
      "definition": {
        "table": "public.items",
        "root_table_id": 16385,
        "primary_key": ["id"],
        "replica": "default",
        "log_mode": "full",
        "where": "status = 'active'",
        "columns": ["id", "name", "status"],
        "storage": {"compaction": "disabled"},
        "flags": {},
        "dependency_handles": []
      },
      "status": {
        "snapshot_started": true,
        "snapshot_completed": true
      },
      "latest_offset": "0_0",
      "pg_snapshot": {
        "xmin": 12340,
        "xmax": 12342,
        "xip_list": [12341]
      }
    }
  ]
}

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
2119	1	2118	0

View the top 2 failed test(s) by shortest run time

Elixir.Electric.Plug.MetadataSnapshotPlugTest::test /v1/metadata-snapshot GET returns comprehensive metadata snapshot

Stack Traces | 0.169s run time

6) test /v1/metadata-snapshot GET returns comprehensive metadata snapshot (Electric.Plug.MetadataSnapshotPlugTest)
     .../electric/plug/metadata_snapshot_plug_test.exs:30
     Assertion with < failed, both sides are exactly equal
     code: assert db["xmin"] < db["xmax"]
     left: 2192
     stacktrace:
       .../electric/plug/metadata_snapshot_plug_test.exs:51: (test)

Elixir.Electric.Plug.LowPrivilegeRouterTest::test /v1/shapes with manual publication management GET fails to create initial snapshot when Electric cannot read from the table

Stack Traces | 0.183s run time

2) test /v1/shapes with manual publication management GET fails to create initial snapshot when Electric cannot read from the table (Electric.Plug.LowPrivilegeRouterTest)
     .../electric/plug/low_privilege_router_test.exs:47
     Assertion with == failed
     code:  assert {503, %{"message" => "Unable to create initial snapshot: permission denied for table items"}} ==
              get_shape(ctx)
     left:  {503, %{"message" => "Unable to create initial snapshot: permission denied for table items"}}
     right: {409, [%{"headers" => %{"control" => "must-refetch"}}]}
     stacktrace:
       .../electric/plug/low_privilege_router_test.exs:65: (test)

To view more test analytics, go to the Test Analytics Dashboard
_{📋 Got 3 mins? Take this short survey to help us improve Test Analytics.}

[blacksmith-sh]

Found 5 test failures on Blacksmith runners:

Failures

Test	View Logs
Elixir.Electric.Plug.LowPrivilegeRouterTest/test /v1/ shapes with manual publication management GET fails to create initial snapshot when Ele ctric cannot read from the table	View Logs
Elixir.Electric.Plug.MetadataSnapshotPlugTest/test /v1/ metadata-snapshot GET returns comprehensive metadata snapshot	View Logs
Elixir.Electric.Plug.MetadataSnapshotPlugTest/test /v1/ metadata-snapshot GET returns comprehensive metadata snapshot	View Logs
Elixir.Electric.Plug.MetadataSnapshotPlugTest/test /v1/ metadata-snapshot GET returns comprehensive metadata snapshot	View Logs
Elixir.Electric.Plug.MetadataSnapshotPlugTest/test /v1/ metadata-snapshot GET returns comprehensive metadata snapshot	View Logs