fix(session): serialize concurrent schema migrations

[senamakel]

Summary

Fix the schema migration race identified after #141 merged and document the new reasoning persistence API. Each migration now re-reads schema_version after acquiring BEGIN IMMEDIATE, so a connection with a stale migration plan skips DDL another connection already applied.

Follow-up to #141 and its review threads.

API Or Behavior Changes

• Concurrent first-open/upgrade connections no longer repeat non-idempotent DDL.
• No public API shape changes beyond feat(session): persist assistant reasoning content #141.
• Session README now documents record_message_with_reasoning and durable optional reasoning content.

Tests

• cargo fmt --check
• cargo clippy -p tinyagents-session -- -D warnings
• N/A: cargo clippy --all-targets -- -D warnings is covered by upstream CI; the changed crate passes strict Clippy.
• N/A: cargo clippy --all-targets --all-features -- -D warnings is covered by upstream CI; the changed crate passes strict Clippy.
• N/A: cargo build --all-targets is covered by upstream CI; targeted package compilation completed through tests and Clippy.
• N/A: cargo build --all-targets --all-features is covered by upstream CI; targeted package compilation completed through tests and Clippy.
• cargo test -p tinyagents-session stale_migration_plan_rechecks_version_after_lock
• cargo test -p tinyagents-session assistant_reasoning_round_trips_separately_from_visible_content
• N/A: cargo test --all-features is covered by upstream CI; focused migration and persistence regressions passed.

Documentation

Updated crates/tinyagents-session/src/README.md and migration module docs with the public recording API, persisted column, and lock/recheck invariant.

[coderabbitai]

Important

Approval pending

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-31T19:29:40.475317Z	63dc528	New commits

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[tinysweeper]

tinysweeper found nothing blocking. Approving.

             $0.0043 · 52,870 in / 407 out · 0 cached (0%) · openrouter/openai/text-embedding-3-small, deepseek/deepseek-v4-flash · 257 embedded
critique:    $0.0019 · 23,429 in / 158 out · 0 cached (0%) · deepseek/deepseek-v4-flash
security:    $0.0010 · 12,213 in / 94 out  · 0 cached (0%) · deepseek/deepseek-v4-flash
tests:       $0.0010 · 12,557 in / 92 out  · 0 cached (0%) · deepseek/deepseek-v4-flash
description: $0.0004 · 4,671 in  / 63 out  · 0 cached (0%) · deepseek/deepseek-v4-flash

[tinysweeper]

How this change flows

0 changed behaviours across 9 relationships. 5 surrounding behaviours are shown (60 graph nodes walked). 47 further behaviours left out to keep the diagram readable.

flowchart LR
  n0["with_memory_connection"]:::impacted
  n1["insert_test_session"]:::impacted
  n2["execute"]:::impacted
  n3["search_sessions_inner"]:::impacted
  n4["search_by_fts_query"]:::impacted
  n1 -->|calls| n2
  n4 -->|calls| n0
  n4 -->|tests| n0
  n4 -->|calls| n1
  n4 -->|tests| n1
  n4 -->|calls| n2
  n4 -->|tests| n2
  n4 -->|calls| n3
  n4 -->|tests| n3
  classDef changed fill:#0d4429,stroke:#238636,color:#e6edf3
  classDef impacted fill:#161b22,stroke:#6e7681,color:#c9d1d9
  classDef flagged fill:#5a1e02,stroke:#d93f0b,color:#ffffff
  classDef blocking fill:#67060c,stroke:#f85149,color:#ffffff

Loading

_{Green: changed behaviour. Grey: surrounding behaviour. Arrows name the call, use, implementation, or test relationship. Orange: has findings. Red: has a finding that blocks the merge.}

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: e8c3c7c655

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