GES Extension: Stream export (JSONL interchange)

Part of the Git Event Store specification family. Extends the core specification (../git-event-store-spec.md); RFC-2119 keywords per core §0.1. An implementation claims this extension per core §1. Section and requirement numbering is retained from the pre-family document for E-ID and cross-reference stability.

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16d. Stream export (JSONL interchange)

16d.1. Implementations SHOULD provide export of a stream (or range) as JSONL — one event record per line — produced entirely by plumbing over the object store, without checking out any branch (no HEAD, index, or working-tree change). This is the sanctioned way to obtain a file-/stream-shaped, tool-friendly view and replaces working-tree materialization (§6.3.5.4).

16d.2. Mechanism. Enumerate the stream’s commits in ancestry (event) order (git rev-list --reverse <stream-ref>, optionally bounded by <snapshot>..<tip> or by position); resolve each commit’s single event blob (git ls-tree); and stream blob contents through a single long-lived git cat-file --batch to avoid per-event process forks (§11.6), emitting each record minified to one line terminated by \n. Output MUST be streamed, not buffered whole.

16d.3. Self-contained lines. Each emitted line MUST be a complete event record (§6.2). If the stored record was minimized (§6.3.3), the exporter MUST re-inject the header-derived fields so every line stands alone.

16d.4. Ordering and range. Lines MUST be in event order; range export maps to readStream bounds (§10.2).

16d.5. Interchange seam. The JSONL stream is the seam to external tooling — jq, DuckDB (read_json), other event stores, backups. A symmetric import (JSONL → appendToStream) MAY be provided for seeding/migration and, if provided, MUST honor concurrency (§9.2) and idempotency (§8.2.2).

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Requirements (EARS)

Moved verbatim from the companion catalog (../ges-review-and-ears.md); IDs unchanged.

• E-16d-1a Where export is offered, the exporter shall produce one self-contained JSON record per line in event order. (test 23)
• E-16d-1b Where export is offered, the exporter shall not perform any checkout. (test 23)
• E-16d-2 The exporter shall stream output rather than buffer the whole stream.
• E-16d-3 When the stored record was minimized, the exporter shall re-inject the header-derived fields so each line stands alone.
• E-16d-4a Where import is offered, the store shall apply each imported event through the append path under concurrency control (§9.2).
• E-16d-4b Where import is offered, the store shall deduplicate imported events by id (§8.2.2).