BE-846: atlas: delta feed, placement and projector

[indietyp]

🌟 What is the purpose of this PR?

Add the delta pipeline that keeps a generation's overlay live, from the feed through placement and projection to the task that runs them. A delta feed bound to one process-wide atlas and a single epoch cannot run per generation, and a second generation has no feed of its own. Here a generation's feed runs against its own World, and each published revision is a new Epoch.

The module stays dead code under the lib.rs attribute until the read API consumes it (BE-815).

For review, the properties this stands on:

• The feed reads arrivals from the store and the placement task positions them, after which the projector maps their embeddings onto the layout. The task lifecycle runs all of it and publishes each revision as a new Epoch.
• The feed starts, stops and joins on its own.
• A walk delivers a captured schedule with the rows an epoch refuses removed, and every bucket run stays contiguous.

🔍 What does this change?

• serve/delta/feed/: DeltaReader and the pending queue.
• serve/delta/placement/: DeltaPlacementTask and its pending set.
• serve/delta/projector/: DeltaProjector over the EmbeddingWorkflow.
• serve/delta/task/: DeltaTask with its options, the lifecycle that runs the three and publishes.
• serve/walk/: Walk over a captured schedule.
• Each module carries its tests beside it.

❓ How to test this?

1. cargo nextest run -p hash-graph-atlas --all-features serve::delta:: runs the feed, placement, projector and task tests, including the start, stop and join cases.
2. Reading order: serve/delta/task/mod.rs is the lifecycle, and the other three are what it drives.

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• does not modify any publishable blocks or libraries, or modifications do not need publishing

📜 Does this require a change to the docs?

The changes in this PR:

• are internal and do not require a docs change

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• do not affect the execution graph

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[codecov]

Codecov Report

❌ Patch coverage is 66.51292% with 363 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.84%. Comparing base (192ab0c) to head (c999864).

Files with missing lines	Patch %	Lines
...local/graph/atlas/src/serve/delta/placement/mod.rs	43.36%	122 Missing and 6 partials ⚠️
...ibs/@local/graph/atlas/src/serve/delta/feed/mod.rs	58.02%	98 Missing and 4 partials ⚠️
...local/graph/atlas/src/serve/delta/projector/mod.rs	57.43%	81 Missing and 2 partials ⚠️
...ibs/@local/graph/atlas/src/serve/delta/task/mod.rs	80.58%	19 Missing and 1 partial ⚠️
libs/@local/graph/atlas/src/serve/walk/mod.rs	57.89%	16 Missing ⚠️
...al/graph/atlas/src/serve/delta/feed/pending/mod.rs	93.03%	8 Missing and 6 partials ⚠️

Additional details and impacted files

@@                                        Coverage Diff                                         @@
##           bm/be-845-atlas-world-epoch-and-schedules-of-the-serving-layer    #9710      +/-   ##
==================================================================================================
+ Coverage                                                           68.72%   68.84%   +0.12%     
==================================================================================================
  Files                                                                1114     1121       +7     
  Lines                                                              101466   102550    +1084     
  Branches                                                             5000     5073      +73     
==================================================================================================
+ Hits                                                                69729    70602     +873     
- Misses                                                              30888    31079     +191     
- Partials                                                              849      869      +20     

Flag	Coverage Δ
apps.hash-ai-worker-ts	1.99% <ø> (ø)
apps.hash-api	15.35% <ø> (ø)
apps.hash-graph	13.62% <ø> (ø)
rust.hash-graph-atlas	80.80% <66.51%> (-0.01%)	⬇️

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[cursor]

PR Summary

Medium Risk
New concurrent replay path over Postgres, placement, and optional Temporal workflows affects how live entities enter the layout, though it remains unwired from the public API until BE-815.

Overview
Introduces the Atlas live-delta pipeline so a generation's overlay can track Postgres entity arrivals: poll and coalesce events, classify nodes/edges, resolve displays, request wire positions, and publish each revision as a new Epoch via DeltaReader.

DeltaFeedTask replays safety-lagged entity events, stages per-entity work in Pending (overlap by transaction time, withdrawals, version-checked placement completions), and exchanges the working Delta through a coalescing Publication loop.

DeltaPlacementTask admits placement requests, polls DB embeddings with retry budgets, optionally starts Temporal embedding workflows, projects batches on Rayon through DeltaProjector, and returns fitted-world positions or terminal **PlacementError**s.

DeltaTask opens the projector (checkpoint + roundtrip sample when present), wires feed ↔ placement channels, and runs feed, publication, and placement workers until shutdown.

Extensive unit tests cover pending/feed/placement/projector edge cases. Unrelated test fixtures in salt/fit/tests.rs rename the sample reviewer to Max Mustermann.

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Type change keeps both identities live

Medium Severity

apply writes a node or edge from the latest classification without withdrawing the other identity. After an entity's type flips between link and non-link, classify follows the new kind, and both the old row and the new one stay visible in the published overlay.

Additional Locations (1)

• libs/@local/graph/atlas/src/serve/delta/feed/pending/mod.rs#L201-L214

 

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