fix(checkpoint): cap full upstream cursor at 512 characters

[miyaontherelay]

Checkpoint upstream cursor validation now rejects 513-character tokens and caps the complete token at 512 characters. The upstream:v1: prefix is 12 characters, so the tail bound is 500; #532 used 501. Updated all three Go validators, OpenAPI patterns, and boundary tests consistently.

Validation: checkpoint pattern, verify, handback and resume Go tests pass across mountsync, relayfile and CLI; the full relevant suites passed for #532. This correction follows #532 and should be included before publishing the mount/CLI prerequisite for relayfile-cloud#293. No release triggered.

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Note

Low Risk
Tightens validation only; cursors at the previous 513-character boundary would now be rejected, aligning clients and API with the intended 512-character cap.

Overview
Corrects an off-by-one in checkpoint eventCursor validation so the full upstream:v1: token is capped at 512 characters (12-character prefix + 500-character tail), not 513.

The same regex bound is applied in the CLI (checkpointCursorPattern), mount sync, relayfile seal store, and three OpenAPI eventCursor patterns. Boundary tests now treat a 500-character tail as valid and reject 501+.

^{Reviewed by Cursor Bugbot for commit af61cc4. Bugbot is set up for automated code reviews on this repo. Configure here.}

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Reviewing files that changed from the base of the PR and between 447250e and 3283f9d.

📒 Files selected for processing (7)

• cmd/relayfile-cli/checkpoint_lifecycle.go
• cmd/relayfile-cli/checkpoint_lifecycle_test.go
• internal/mountsync/syncer.go
• internal/mountsync/syncer_test.go
• internal/relayfile/checkpoint_seal.go
• internal/relayfile/checkpoint_seal_test.go
• openapi/relayfile-v1.openapi.yaml

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📝 Walkthrough

Walkthrough

The upstream:v1: cursor suffix limit changes from 501 characters to 500 in validation patterns and OpenAPI schemas. Boundary tests now accept 500 characters and reject 501.

Changes

Upstream cursor length limit

Layer / File(s)	Summary
Cursor validation and boundary tests internal/relayfile/checkpoint_seal.go, cmd/relayfile-cli/checkpoint_lifecycle.go, internal/mountsync/syncer.go, openapi/relayfile-v1.openapi.yaml, internal/relayfile/checkpoint_seal_test.go, cmd/relayfile-cli/checkpoint_lifecycle_test.go, internal/mountsync/syncer_test.go	The cursor patterns and three OpenAPI schema constraints now limit upstream suffixes to 500 characters. Tests accept a 500-character suffix and reject a 501-character suffix.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Suggested reviewers: khaliqgant

Merge Risk: ⚪ Minimal · up to 3283f

The cursor limit is consistently capped at 512 characters including its prefix, with tests for the 500/501-character suffix boundary. No material merge risk is evident.

🚥 Pre-merge checks | ✅ 4 | ❓ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	❓ Inconclusive	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 5 files. (2 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: the full upstream cursor is capped at 512 characters.
Description check	✅ Passed	The description directly explains the 512-character cap, the off-by-one correction, the affected validators and OpenAPI patterns, and the boundary tests.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 5 files. (2 skipped: 1 unsupported, 1 too large.)

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_{A rabbit checks the cursor line
Five hundred marks now fit just fine
At five-oh-one, the tests say no
The schemas match the rules below
Then hops away through fields of snow}

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

[github-actions]

Relayfile Eval Review

Run: .relayfile/evals/runs/2026-10-08T18-09-42-345Z-HEAD-provider
Mode: provider
Git SHA: 95fe151

Passed: 4 | Needs human: 0 | Reviewable: 0 | Missing output: 0 | Failed: 0 | Skipped: 0

Human Review Cases

No reviewable human-review cases captured Relayfile output.

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No issues found across 7 files

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