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name: backend-import-export-pipeline description: Slack-MM2 Sync import/export pipeline rules: single-pass deterministic importer, monotonic progress counters, merge_job_meta semantics, and exporter dependency order. Use when modifying importer/exporter stages or progress behavior. license: Complete terms in LICENSE.txt

Import/Export Pipeline (Backend)

This skill encodes the project’s core invariants for the unified single-pass pipeline and deterministic progress tracking.

When to use

• Changing import stages, progress reporting, or ImportJob.meta
• Adding new counters (*_processed, *_exported) or changing counter semantics
• Modifying exporter orchestration order or entity dependency logic
• Debugging progress bars / “early success” behavior used by integration checks

Canonical pipeline (single pass)

Stages:

• extracting → users → channels → messages → ready_export → exporting → done

Key rule:

• Reactions/attachments/custom-emoji references are captured during the single pass through messages (no separate reaction/attachment stages).

Deterministic progress invariants

• All ingestion counters (*_processed) are monotonically non-decreasing.
• When transitioning to exporting / done, the backend freezes denominators in meta.totals and sets totals_frozen=true.
• Frontend export progress should use *_exported against meta.totals.*.

Atomic meta updates (merge_job_meta)

To avoid lost updates on JSONB meta, updates must be atomic (single SQL UPDATE) using the project’s merge builder semantics:

• incr: atomic increment
• max: monotonic maximum (safety)
• set: set exact values (stage, flags)
• nested: merge nested objects (e.g., totals, durations_ms)
• remove: remove keys (rare)

Rule of thumb:

• Do NOT implement ORM “read-modify-write” loops for meta.

Export ordering

Global type barrier order:

• user → custom_emoji → channel → message → attachment → reaction

Meaning:

• A later type must not start exporting until previous type has no remaining pending entities across jobs in exporting.

If you add a new counter or entity type

Checklist:

• Update the importer to increment the new *_processed counter only after the entity meets base invariants.
• Update export logic and/or exported counters if the frontend needs export progress for that type.
• Update docs where counters are described.
• Update the mini-backup regression expected values if it changes deterministic totals.

Related docs

• Pipeline + dev workflow notes: docs/dev.md
• Backend overview: backend/README.md
• Import stages + counters implementation: backend/app/services/backup/orchestrator.py
• Atomic meta updates implementation: backend/app/services/backup/meta_utils.py
• Export module overview: backend/app/services/export/README.md
• Export ordering implementation: backend/app/services/export/orchestrator.py