fix(tui): preserve subcent costs during aggregation

[jimyag]

Summary

Prevent low per-message costs from rounding to zero before daily and session aggregation. TUI statistics now retain micro-dollar precision internally while preserving the existing costCents JSON output.

Changes

• retain micro-dollar precision in TuiStats add, subtract, and conversion paths
• repack single-message contribution costs in microdollars without increasing the 32-byte cache entry
• add regression coverage for daily, session, packed-message, and JSON serialization paths
• include the same model-filter conversation assertion correction as feat(analyzers): add DeepSeek Harness support #236 so both PRs remain independently green; the duplicate patch should merge cleanly whichever lands first

Verification

• cargo build --quiet
• cargo test --quiet (419 passed)
• cargo clippy --locked --all-targets --quiet -- -D warnings
• cargo doc --quiet
• cargo fmt --all --quiet
• bash scripts/license-checks.sh
• git diff --check

Notes

• TuiStats grows from 40 to 48 bytes to retain exact internal cost precision.
• SingleMessageContribution remains 32 bytes.
• Reviewer focus: micro-dollar rounding and the revised packed bitfield boundaries.

Summary by CodeRabbit

• Improvements

  • Cost tracking now preserves sub-cent precision when aggregating message and session costs.
  • Larger cost values are handled safely without overflow.
  • Existing cent-based cost displays and serialized output remain compatible, with values rounded appropriately.

• Bug Fixes

  • Corrected rounding and accumulation for small costs across conversations, sessions, and statistics.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 21e6c4de-fa78-4854-9130-2bf30a7ebfbb

📥 Commits

Reviewing files that changed from the base of the PR and between c843248 and a4d7588.

📒 Files selected for processing (7)

• src/contribution_cache/single_message.rs
• src/contribution_cache/tests/compact_stats.rs
• src/contribution_cache/tests/single_session.rs
• src/tui.rs
• src/tui/tests.rs
• src/types.rs
• src/utils/tests.rs

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📝 Walkthrough

Walkthrough

The change adds exact microdollar cost storage to TuiStats, preserves costCents serialization, expands packed cost capacity, and updates contribution, session, date aggregation, conversion, and regression tests for sub-cent precision.

Changes

Microdollar cost handling

Layer / File(s)	Summary
Exact TuiStats cost model src/types.rs, src/tui.rs, src/tui/tests.rs	TuiStats stores microdollars internally, rounds cents for serialization, and uses saturating arithmetic. Model conversion and tests use the updated cost path.
Packed contribution cost round-trip src/contribution_cache/single_message.rs, src/contribution_cache/tests/compact_stats.rs	PackedStatsDate stores a 30-bit cost_micros field. Packing and unpacking preserve microdollar values and saturate at the field limit.
Aggregate precision regression coverage src/contribution_cache/tests/single_session.rs, src/utils/tests.rs	Session and date aggregation tests verify that sub-cent costs remain precise while cent totals round correctly.

Estimated code review effort: 4 (Complex) | ~45 minutes

Mergeability Score: ⚪ Minimal · up to a4d75

The PR preserves micro-dollar precision internally while keeping the existing JSON output contract, and no actionable merge-blocking risk remains after normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant Stats
  participant TuiStats
  participant PackedStatsDate
  participant Aggregation
  Stats->>TuiStats: set_cost(dollars)
  TuiStats->>TuiStats: store exact microdollars
  TuiStats->>PackedStatsDate: pack cost_micros
  PackedStatsDate->>TuiStats: restore with set_cost_micros
  Aggregation->>TuiStats: add exact microdollar costs
  TuiStats-->>Aggregation: expose precise cost and rounded costCents

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Possibly related PRs

• Piebald-AI/splitrail#130: Both changes modify TuiStats cost handling and address cost-field capacity.
• Piebald-AI/splitrail#132: Both changes modify the integer representation of TuiStats cost data.
• Piebald-AI/splitrail#189: Both changes update TUI statistics and related conversion tests.

Suggested reviewers: mike1858, basekevin

Poem

I’m a rabbit with microdollars to spare,
Packing small costs with careful repair.
Sub-cent crumbs stay in the sum,
While cents round neatly for everyone.
Hop, hop—precision has come!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: preserving sub-cent costs during TUI aggregation.
Docstring Coverage	✅ Passed	Docstring coverage is 92.31% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[jimyag]

before

after

[mike1858]

It's really not so small a difference! It's because the project was made at a time when models followed instructions much worse than they do now—like rounding small numbers to zero. 0.04 !== 0.00.