feat(cost): surface cost-by-phase in the model usage dashboard (P5.T3)

[OBenner]

What

Roadmap P5·T3: «Дашборд: посчитать $ … + строку Cost … «Сборка стоила $X — планирование/код/QA»».

The backend model_usage_summary.json already carries cost_by_phase (from P5·T2), but the IPC transformSummary() dropped it and no UI surfaced a per-phase cost breakdown.

• model-usage-handlers.ts — pass cost_by_phase through transformSummary (already present in the --get-summary output). Frontend-cached summaries written before this field simply render no section and self-heal on the existing 5-min cache TTL.
• ModelUsageSummary type — optional cost_by_phase field.
• new pure orderPhaseCosts() helper — pipeline order (planning → coding → test_generation → validation → profiling), unknown keys appended alphabetically, non-positive/non-finite dropped.
• ModelUsageDashboard — a "Cost by Phase" card (planning / coding / QA / … with $ amounts), i18n en/fr including phase labels (validation → "QA").

Deviation from the roadmap's named file

The roadmap said the cost line goes in ContextViewer.tsx, but ContextViewer is dead code — it's mounted nowhere in the renderer (only its main-process handlers + preload API exist). The genuinely visible, sidebar-reachable cost surface is the Model Usage dashboard (activeView === 'model-usage', shortcut O), which already shows total/per-agent/per-model cost — so the per-phase breakdown lands there.

Acceptance

Model Usage → Cost by Phase: Planning $X · Coding $Y · QA $Z · …, sourced from the real backend cost_by_phase.

Tests

• 5 new in phase-costs.test.ts (pipeline ordering / zero+negative+NaN filtering / unknown-key ordering / empty-null-undefined).
• Electron tsc 0, biome clean. Reviewed by a 2-lens adversarial workflow — 0 confirmed findings (both raised nits verified false: the $X.XX format matches the file's existing total_cost rendering; test_generation is intentional forward-compat).

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added a new Cost by Phase section in the Model Usage dashboard to show spending broken down by execution phase.
  • Phase labels are now localized and displayed in a consistent order, with unknown phases still shown.

• Bug Fixes

  • Improved handling of phase-cost data so empty, missing, or invalid values no longer appear in the dashboard.
  • Older saved usage summaries continue to work even if phase-cost data is unavailable.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a cost_by_phase field to the model usage backend handler and shared type, introduces a new orderPhaseCosts utility with tests for ordering/filtering phase costs, renders a "Cost by Phase" section in the Model Usage dashboard with new i18n strings, and updates roadmap documentation.

Changes

Cost by Phase Feature

Layer / File(s)	Summary
Type contract and data shape apps/frontend/src/shared/types/model-usage.ts, apps/frontend/src/renderer/lib/phase-costs.ts	Adds cost_by_phase optional field to ModelUsageSummary, and defines PhaseCost interface with PHASE_ORDER constant.
Backend passthrough and ordering utility apps/frontend/src/main/ipc-handlers/model-usage-handlers.ts, apps/frontend/src/renderer/lib/phase-costs.ts, apps/frontend/src/renderer/__tests__/phase-costs.test.ts	transformSummary populates cost_by_phase; orderPhaseCosts filters non-positive/non-finite costs, orders known phases by pipeline order, and appends unknown phases alphabetically; tests cover empty input, ordering, filtering, and edge cases.
Dashboard UI and localization apps/frontend/src/renderer/components/model-usage/ModelUsageDashboard.tsx, apps/frontend/src/shared/i18n/locales/en/model-usage.json, apps/frontend/src/shared/i18n/locales/fr/model-usage.json	Dashboard renders a "Cost by Phase" card using orderPhaseCosts, with i18n phase labels and formatted dollar costs; en/fr locale files add dashboard.costByPhase and dashboard.phases entries.
Roadmap documentation update docs/strategy/roadmap.md	Roadmap replaces prior ContextViewer-based cost plan with the Cost by Phase dashboard approach and marks a corresponding checklist item complete.

Estimated code review effort: 2 (Simple) | ~15 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Backend
  participant Handler as transformSummary
  participant Dashboard as ModelUsageDashboard
  participant OrderUtil as orderPhaseCosts

  Backend->>Handler: raw.cost_by_phase
  Handler->>Dashboard: summary.cost_by_phase
  Dashboard->>OrderUtil: orderPhaseCosts(summary.cost_by_phase)
  OrderUtil-->>Dashboard: ordered PhaseCost[]
  Dashboard-->>Dashboard: render Cost by Phase card

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Related Issues: Not specified in the provided context.

Related PRs: References PR #361 in roadmap documentation.

Suggested labels: frontend, i18n, documentation

Suggested reviewers: Not specified in the provided context.

🐰 A phase, a cost, a tidy row,
Ordered neatly, watch them grow,
Planning, coding, tests align,
A dashboard card now looks so fine,
Hop along, the numbers show! 🥕

🚥 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 summarizes the main change: adding cost-by-phase visibility to the Model Usage dashboard.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/p5-cost-dashboard

Warning

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Failed to run tools: 13 INTERNAL: Received RST_STREAM with code 2 (Internal server error)

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@apps/frontend/src/renderer/components/model-usage/ModelUsageDashboard.tsx`:
- Around line 337-366: The Cost by Phase section is rendered via an inline IIFE
inside JSX instead of a dedicated component, which breaks the existing
composition pattern used in ModelUsageDashboard. Extract the phase-cost
calculation and conditional rendering into a small CostByPhaseCard component (or
similarly named component), and have ModelUsageDashboard pass
summary.cost_by_phase and t into it, mirroring the structure used by
ModelUsageCard and ModelListSection.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: c2d3801c-3a99-4698-b6a7-2ad06ba30929

📥 Commits

Reviewing files that changed from the base of the PR and between e0836ed and 707de76.

📒 Files selected for processing (8)

• apps/frontend/src/main/ipc-handlers/model-usage-handlers.ts
• apps/frontend/src/renderer/__tests__/phase-costs.test.ts
• apps/frontend/src/renderer/components/model-usage/ModelUsageDashboard.tsx
• apps/frontend/src/renderer/lib/phase-costs.ts
• apps/frontend/src/shared/i18n/locales/en/model-usage.json
• apps/frontend/src/shared/i18n/locales/fr/model-usage.json
• apps/frontend/src/shared/types/model-usage.ts
• docs/strategy/roadmap.md

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud