perf(pl-tree): cut the cost of applying a tree update

[xnacly]

Makes PlTreeState.updateFromResourceData, the apply step of a tree-sync poll, faster.

Changes

• 5126c71 Notify resourcesAdded once per update instead of once per new resource.
  → 21% faster on a first load, nothing on a steady poll.
• f3d0776 Walk stored fields in lockstep with the incoming ones, matching by direct name
  comparison instead of a fieldsMap hash lookup per field — poll-response field names are
  freshly decoded, so V8 has to hash every one. → 10% faster on a steady poll.
• c64783a Same lockstep walk for KV entries. → 2% faster on a steady poll.
• d56e597 Hoist the transition-error snapshot out of the patch loop, dropping a closure
  and a basicState clone per resource per update. → 4% faster on a steady poll.

Improvement

Per apply, at 10,000 resources with ~10 fields and 2 KV entries each:

update contains	faster by
first load, every resource new	23%
steady poll, everything held and unchanged	11%
field added and removed on 10% of resources	13%
field value repointed on 10% of resources	11%
2% of resources drop child refs, cascading through collectGarbage	12%

Greptile Summary

This PR optimizes the in-memory apply phase of tree synchronization while retaining existing field, KV, reference-count, watcher, and transition-validation behavior.

Important touched terms

• PlTreeState.updateFromResourceData — Applies incoming resource snapshots to the local tree. It now batches resource-added notification, uses lockstep field/KV traversal, and reuses transition-error diagnostic machinery.
• PlTreeResource — The stored representation of one resource and its mutable state. Its pre-update state is now captured through scalar diagnostic variables rather than cloning basicState for every resource.
• fieldsMap — A name-keyed map of a resource’s fields. Incoming fields now take a direct iterator fast path while order matches, then fall back to map lookup after any divergence.
• KV entries (resource.kv) — Per-resource string keys mapped to binary values. Their synchronization now uses the same lockstep fast path, abandoning it before inserting into the map.
• resourcesAdded — The change source watched when a requested resource is absent. It is now marked once after an update rather than once for every newly created resource.
• unexpectedTransitionError — Invalidates the tree and reports an illegal resource-state transition. Its closure and immutable diagnostic setup are now allocated once per update.
• Reference counts — Counts that retain resources reachable through fields. New tests verify that field reordering and repointing do not inflate these counts or prevent garbage collection.
• Watcher invalidation — Notification that observed tree state changed. New tests ensure pure field and KV reordering does not spuriously invalidate watchers.

Additional changes

• Adds focused regression coverage for reordered, inserted, removed, and repointed fields; KV reorder/update/deletion; typed-field removal; and reference-count integrity.
• Adds a patch changeset documenting the measured tree-apply performance improvement.

Confidence Score: 5/5

The PR appears safe to merge, with the optimized paths preserving existing observable behavior and receiving focused regression coverage.

No actionable correctness, security, or repository-rule issue remains; exact-name fallback protects divergent field and KV ordering, batched notification preserves watcher semantics, and the diagnostic snapshot matches the prior pre-mutation state.

Important Files Changed

Filename	Overview
lib/node/pl-tree/src/state.ts	Introduces notification batching, lockstep field/KV traversal, and reusable transition-error diagnostics without changing established update semantics.
lib/node/pl-tree/src/state.test.ts	Adds targeted tests for order divergence, watcher stability, field lifecycle, KV synchronization, and reference-count correctness.
.changeset/tree-apply-cost.md	Records a patch release and summarizes the measured apply-phase performance improvement.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Incoming resource snapshots] --> B{Stored resource exists?}
    B -- No --> C[Create resource]
    C --> D[Count newly added resource]
    B -- Yes --> E[Capture mutable pre-update state]
    E --> F[Apply metadata and state transitions]
    F --> G[Walk stored fields in lockstep]
    G --> H{Names still match?}
    H -- Yes --> I[Use iterator value directly]
    H -- No --> J[Fall back to fieldsMap lookup]
    I --> K[Apply field changes and reference deltas]
    J --> K
    K --> L[Walk KV entries in lockstep]
    L --> M{Keys still match?}
    M -- Yes --> N[Use iterator value directly]
    M -- No --> O[Fall back to KV map lookup]
    N --> P[Apply KV changes and deletions]
    O --> P
    D --> Q[After patch loop]
    P --> Q
    Q --> R[Notify resourcesAdded once]
    R --> S[Apply reference deltas and garbage collection]

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_{Reviews (1): Last reviewed commit: "perf(pl-tree): hoist the transition-erro..." | Re-trigger Greptile}

[changeset-bot]

🦋 Changeset detected

Latest commit: 6cfda51

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@milaboratories/pl-tree	Patch
@milaboratories/pl-drivers	Patch
@milaboratories/pl-middle-layer	Patch
@platforma-sdk/test	Patch
@platforma-sdk/pl-cli	Patch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.52%. Comparing base (e027bf0) to head (d56e597).
⚠️ Report is 49 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1813      +/-   ##
==========================================
- Coverage   54.54%   54.52%   -0.02%     
==========================================
  Files         418      418              
  Lines       21936    21936              
  Branches     4913     4913              
==========================================
- Hits        11964    11960       -4     
+ Misses       8533     8532       -1     
- Partials     1439     1444       +5     

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