fix: gracefully compress long session context

[xuy]

[factory:impl issue=ON-10]

Summary

• add proactive session-context compression before long diagnostic chats hit the provider limit
• summarize older turns with Haiku, keep recent turns verbatim, and retry automatically on context-limit failures
• add focused tests for overflow detection, summary injection, transcript truncation, and token estimation

[xuy]

[factory:review issue=ON-10]
Self-review is blocked because the authenticated GitHub account authored this PR, so I requested external review from aoiwelle instead of submitting a GitHub review.

Concise status:

• I found two blocking concerns for the external reviewer to validate: the code only does a single compress-and-retry pass, and restored sessions currently drop compressed_summary and rehydrate full history.

[aoiwelle]

LGTM

[xuy]

[factory:review issue=ON-10]
Self-review is blocked because the authenticated GitHub account authored this PR, so I could not submit the intended REQUEST_CHANGES review on commit d6be28b5553447064660b0014c7d87a9332395bc.

Blocking findings for the external reviewer:

• cargo test --quiet -p noah-desktop --lib fails on the current head. apps/desktop/src-tauri/src/safety/journal.rs:933 still expects 7 serialized SessionRecord fields after adding compressed_summary, and apps/desktop/src-tauri/src/safety/journal.rs:960 still expects schema version 7 after bumping SCHEMA_VERSION to 8.

[xuy]

[factory:review issue=ON-10]
Self-review is blocked because the authenticated GitHub account authored this PR, so I re-requested external review instead of submitting the intended REQUEST_CHANGES review on commit d6be28b5553447064660b0014c7d87a9332395bc.

Blocking findings on the current head:

• cargo test --quiet -p noah-desktop --lib still fails locally.
• apps/desktop/src-tauri/src/safety/journal.rs:933 still asserts obj.len() == 7 after SessionRecord gained compressed_summary and resolved, so the touched serialization test is stale and failing.
• apps/desktop/src-tauri/src/safety/journal.rs:960 still asserts schema version 7 after SCHEMA_VERSION was bumped to 8.

[aoiwelle]

Please fix these tests.

[xuy]

[factory:review issue=ON-10]
Self-approval is blocked because the authenticated GitHub account authored this PR, so I requested external review from aoiwelle on commit a78a27832f9176c8286d1518457dd7a4c1999008 instead of posting the intended approval.

Validation on this head:

• No new blocking findings in the context-compression, restore, or journal-schema paths.
• cargo test --quiet -p noah-desktop --lib passed locally.
• cargo test --workspace --quiet passed locally.

[aoiwelle]

LGTM