Add private mount state directory support

[khaliqgant]

Summary

• add mountsync private state path resolution with --state-dir, exact --state-file override precedence, and mount-kind-separated state IDs
• keep CLI and relayfile-mount command surfaces on private state outside the mounted tree, while preserving legacy in-root defaults for direct internal NewSyncer embedders
• quarantine only the legacy private state file and its known temp variants from the mount root

Scope

Relayfile-first implementation for the PR #1289 mount-state path recursion spec. Cloud mount-script wiring, snapshot pinning, and deploy/release follow-ups are intentionally left for the next sequence.

Tests

• go test ./internal/mountsync ./cmd/relayfile-mount ./cmd/relayfile-cli -count=1

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: eab126f9-6b40-404a-993c-f15c273048c5

📥 Commits

Reviewing files that changed from the base of the PR and between 0f6b856 and d6c5d98.

📒 Files selected for processing (7)

• cmd/relayfile-cli/main.go
• cmd/relayfile-cli/setup_e2e_test.go
• cmd/relayfile-mount/main.go
• cmd/relayfile-mount/main_test.go
• internal/mountsync/state_path.go
• internal/mountsync/state_path_test.go
• internal/mountsync/syncer.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/mount-state-dir

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[gemini-code-assist]

Code Review

This pull request introduces a robust state path resolution and validation mechanism for relayfile mounts, adding support for custom state directories (--state-dir) and mount kinds (--mount-kind), while quarantining legacy state files outside the local mount root. The code review highlights critical issues: sharing a single explicit state file across concurrent scoped mounts can lead to state corruption, and using os.Rename to move legacy state files can fail with EXDEV across different filesystems. Additionally, the reviewer suggests making the legacy quarantine step non-fatal on failure and simplifying the home directory lookup logic.

[github-actions]

Relayfile Eval Review

Run: .relayfile/evals/runs/2026-05-28T12-17-16-260Z-HEAD-provider
Mode: provider
Git SHA: e6b1aed

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.

[khaliqgant]

Addressed the Gemini review feedback in 86c6134:\n\n- reject sharing one explicit --state-file across multiple concurrent scoped mounts; users should use --state-dir for scoped mounts\n- make legacy quarantine robust across filesystems by falling back from rename to copy/remove\n- keep quarantine non-fatal at Syncer startup; it now warns and continues\n\nRe-ran: go test ./internal/mountsync ./cmd/relayfile-mount ./cmd/relayfile-cli -count=1

[cubic-dev-ai]

2 issues found across 7 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>