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CHANGELOG 1.3.10 (unreleased) with behaviour-change and breaking sections, README capability rows and a 1.3.10 section, ARCHITECTURE section 15 plus 6.2/7 updates, schema doc for the stream_end column, migration impact notes, ROADMAP entry, .env.example MISSING_DONE semantics, and a revision pointer on the 1.3.9 design. Follow-ups filed as #32 and #33.