id: "GW20-007"
title: "Keep checkpoint refresh work proportional to the retained suffix"
type: "bug"
status: "planned"
milestone: "v20.1.0"
category: "required"
workstream: "runtime"
issue: "#963"
baseline_commit: "ceb58e656ec5bc85f0ae5991bf2a55599693bbb3"
feedback_sections: [6]
prerequisites: []

Bug

LLM prompt

Complete GW20-007: Keep checkpoint refresh work proportional to the retained suffix.
Read this entire task and its current GitHub issue before implementation.
Verify the current mainline and all prerequisite integrations.
Read AGENTS.md and the three TypeScript policy documents.
Use runtime-backed domain values and injected ports.
Keep parsing and codecs at the adapter boundary.
Preserve v20 APIs, stored identities, CRDT semantics, and failure meanings.
Use one coherent issue, PR, and mainline integration. Do not leave a broken intermediate state.
Reproduce the symptom in Docker. Fill Diagnosis with evidence before fix work.
Test each hypothesis against the actual execution path.
Problem to resolve:
The report records increasing materialize cost across six checkpoints with the same 100-patch suffix. The exact cause remains unmeasured.
Acceptance checks:
Trace checkpoint selection, predecessor inspection, metadata reads, patch decoding, and reduction separately before fix work.
For a valid compatible checkpoint, replay and decode only the suffix. Historical checkpoint count does not trigger a full predecessor scan.
Measure constant 100-patch suffixes at history sizes 101, 201, 401, and 601 with one and many earlier checkpoints.
State hashes and read values equal a fresh replay outside the measured region.
Absent, stale, corrupt, and incompatible checkpoints retain correct explicit recovery behavior.
Read these source paths:
src/domain/services/controllers/MaterializeLiveStrategy.ts
src/domain/services/controllers/RetainedMaterializationResumeStrategy.ts
src/infrastructure/adapters/GitCasMaterializationPredecessorResolver.ts
src/domain/warp/RuntimePatchCollector.ts
Prerequisites: None established. Recheck external readiness.
Scope exclusions: Declare a streaming wrapper bounded, or assume the existing resume paths do not exist.
Run all tests and benchmarks in COPY-based Docker without host repository mounts.
Use the project guarded runner and the shared git-locks authority.
Lock host/heavy-work and the exact worker key together for expensive work.
Limit build caches to 20 GiB, test data to 4 GiB, and logs to 128 MiB.
Require 50 GiB free on host and Docker backing storage before heavy work.
Enforce disk accounting, CPU, memory, timeout, and child-process shutdown.
Do not start an unguarded workload. Do not bypass a resource refusal.
Require full touched-code coverage for refactors and an all-green manual SSJS scorecard.
Record source, image, command, fixtures, results, limits, and the regression witness.
Commit only your own files. Do not amend, rebase, force, push, or publish without authorization.
Report incomplete or blocked checks. Do not claim completion from a narrow green test.
Link the issue, coherent PR, and actual mainline integration when those actions are authorized.

1. Background Context

Source: FEEDBACK-git-warp.md, sections 6.
The report SHA-256 is 9b15209d51cd705059a9e6bfebf0f6681ff832924c1462b99ff3cfebde6bacae.
The report uses npm git-warp 20.0.0 and git-cas 6.5.11.
Its runtime results come from macOS host experiments. This planning task did not rerun them.
Source review baseline: ceb58e65.

Tracker: #963.

Read these source and test surfaces before work:

• src/domain/services/controllers/MaterializeLiveStrategy.ts
• src/domain/services/controllers/RetainedMaterializationResumeStrategy.ts
• src/infrastructure/adapters/GitCasMaterializationPredecessorResolver.ts
• src/domain/warp/RuntimePatchCollector.ts

2. Observed

The report records increasing materialize cost across six checkpoints with the same 100-patch suffix. The exact cause remains unmeasured.

2b. Expected

Trace checkpoint selection, predecessor inspection, metadata reads, patch decoding, and reduction separately before fix work.

2c. Reproduction

Source report: experiments/07-performance/checkpoint-scaling.ts and results/07-checkpoint-scaling.json. Not rerun here.

Golden regression: Compare repeated checkpoint cycles in a closed Runtime, an open Runtime, and the supported maintenance path. Count processes and loaded patches.

2d. Blast radius

Population: operators that refresh checkpoints over growing retained histories.
Observed population count: unknown. The report measures fixtures, not deployed users.
No user-count query exists in this task. Do not infer a count from fixture size.
Since: reported in v20.0.0 on 2026-10-06. The introducing commit remains unverified.
Downstream: The report records increasing materialize cost across six checkpoints with the same 100-patch suffix. The exact cause remains unmeasured.

2e. Hypothesis

Predecessor enumeration or replay-basis reconstruction grows with history. MaterializeLiveStrategy already selects checkpoints and suffix streams. Reject each hypothesis with a production-path trace before choosing a fix.

2f. Diagnosis

3. Prerequisites

None established as an internal issue dependency. Verify the current boundary and external readiness before activation.

4. Scope

In: The report records increasing materialize cost across six checkpoints with the same 100-patch suffix. The exact cause remains unmeasured.

Out: Declare a streaming wrapper bounded, or assume the existing resume paths do not exist.

Safe intermediate state: one independently mergeable PR passes its relevant checks after its prerequisites.
Existing supported applications remain usable. Historical data remains intact.

5. Why now

This flaw blocks a supported Synapse store workflow or gives its operator incorrect guidance.
Resolve it within v20.1.0 without reducing the existing causal-history commitment.

6. Risks

Source inspection does not establish runtime or performance results.
Preserve historical identities, validation, and evidence. Do not weaken refusal to obtain a green result.
If the fix requires a breaking contract, record the conflict before activation. Do not hide it within a minor release.

7. Definition of Done

A reproducible regression fails on the baseline and passes on the candidate.

• Trace checkpoint selection, predecessor inspection, metadata reads, patch decoding, and reduction separately before fix work.
• For a valid compatible checkpoint, replay and decode only the suffix. Historical checkpoint count does not trigger a full predecessor scan.
• Measure constant 100-patch suffixes at history sizes 101, 201, 401, and 601 with one and many earlier checkpoints.
• State hashes and read values equal a fresh replay outside the measured region.
• Absent, stale, corrupt, and incompatible checkpoints retain correct explicit recovery behavior.

Golden: Compare repeated checkpoint cycles in a closed Runtime, an open Runtime, and the supported maintenance path. Count processes and loaded patches.

Edges: Exact retained hit; predecessor hit and miss; receipt and diff options; new writer; divergent frontier; corrupt replay basis.

All acceptance checks have evidence from the exact candidate.
Relevant lint, typecheck, compatibility, and Docker checks pass.
The manual SSJS scorecard is green. Refactor coverage reaches 100% on touched code.
Record the issue, PR, and mainline integration commit. Record any external release gate.
A required check with missing evidence remains incomplete.

8. Stakeholders

James Ross: git-warp maintainer and acceptance owner.
Synapse store authors: applications need correct writes, reads, history, and operational guidance.
Library and CLI consumers: existing v20 contracts must remain usable.

9. Related Issues

• #848
• #849
• #851