Harden session cwd resume precedence

[nestharus]

Summary

• Preserve live external-provider runtime cwd as authoritative on resume.
• Keep invocation-recorded cwd as the durable fallback for script/import resume cases with stale mailbox/runtime cwd.
• Add characterization coverage for live runtime cwd beating recorded script-session cwd.

Verification

• cargo fmt --check
• git diff --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test -p oulipoly-runtime session_metadata -- --nocapture
• cargo test -p oulipoly-runtime --test session_metadata_resume_cwd_characterization -- --nocapture
• cargo test -p oulipoly-state provider_session_binding -- --nocapture
• cargo test -p oulipoly-runtime creates_unknown_model_invocation_row -- --nocapture
• cargo test -p oulipoly-runtime passes_parent_invocation_env_to_launcher -- --nocapture
• cargo test -p oulipoly-runtime registers_ingested_session_chain -- --nocapture
• Provider token delta guard: claude delta=-4, codex delta=0

Known Existing Reds

• cargo test --workspace fails on documented pre-existing AGE-245 source guard: s7c_provider_name_grep_invariant_uses_authoritative_manager_baseline.
• bunx tsc --noEmit fails on existing frontend JSX/type baseline issues.