feat: add Claude Opus 4.8 and Claude Fable 5 model support

[Hansen1018]

Summary

Add two new Anthropic models released in 2026: Claude Opus 4.8 (the Opus-4.x refresh) and Claude Fable 5 (Anthropic's first public Mythos-class model, above Opus). Both are reachable via the OpenAI-compatible provider layer, the claw402 x402 paths, and the front-end model selectors.

Models added

Claude Opus 4.8

• API name: claude-opus-4-8
• Released: 2026-05-28
• Context: 1,000,000 tokens
• Max output: 128,000 tokens
• Pricing (same as 4.7): $5.00 / $25.00 per 1M input/output tokens per the anthropic.com news post; per-call estimate USD 0.18/call
• Reference: https://www.anthropic.com/news/claude-opus-4-8

Claude Fable 5

• API name: claude-fable-5
• Released: 2026-06-09
• Tier: First publicly available Mythos-class model (above Opus)
• Context: 1,000,000 tokens
• Max output: 128,000 tokens
• Pricing: $10.00 / $50.00 per 1M input/output tokens (≈2× Opus 4.8 per the news post); per-call estimate USD 0.36/call
• Reference: https://www.anthropic.com/news/claude-fable-5

What changed

File	Change
mcp/provider/claude.go	DefaultClaudeModel → claude-fable-5
api/handler_ai_model.go	claude row's defaultModel → claude-fable-5
mcp/payment/claw402.go	claw402ModelEndpoints gains claude-opus-4-8 and claude-fable-5; legacy claude-opus alias kept
store/ai_charge.go	modelPrices gains claude-opus-4-8 = 0.18 and claude-fable-5 = 0.36
web/src/components/trader/model-constants.ts	Both tiers in CLAW402_MODELS (Fable 5 with 🐉 icon) and BLOCKRUN_MODELS; AI_PROVIDER_CONFIG.claude.defaultModel → claude-fable-5

Diff stat: 5 files changed, 24 insertions(+), 4 deletions(-).

Scope boundary (what did NOT change)

• The claude-opus legacy alias and claude-opus-4-6 entry remain unchanged.
• Other Anthropic models: no change to Haiku / Sonnet lines (only Opus 4.8 + Fable 5 added here, matching what's currently available from the upstream Anthropic news posts).
• Other providers (openai, google, xai, moonshot, etc.) are not touched.
• AICharge table schema unchanged.

Compatibility

• Backward compatible: legacy claude-opus / claude-opus-4-6 / generic claude (Anthropic-API) identifiers keep working and stay selectable.
• Migration needed: no.
• Config / env changes: no.

Default model policy

This PR is the single place where the Anthropic default changes (to Fable 5, Anthropic's currently-flag-ship public model). All WithModel(...) override callers continue to pick any model they want via the existing hook; this PR is purely additive on the model-choice dimension.

Testing

• go build ./... passes
• tsc --noEmit clean (excluding pre-existing StrategyStudioPage.tsx errors that predate this work)

[github-actions]

🤖 Advisory Check Results

These are advisory checks to help improve code quality. They won't block your PR from being merged.

📋 PR Information

Title Format: ✅ Good - Follows Conventional Commits
PR Size: 🟢 Small (28 lines: +24 -4)

🔧 Backend Checks

Go Formatting: ⚠️ Needs formatting

Files needing formatting

api/errors.go
api/handler_wallet.go
cmd/e2e_builder_fee/main.go
market/types.go
mcp/config.go
mcp/context_guard_test.go
mcp/options.go
mcp/payment/claw402.go
mcp/request.go
mcp/request_builder.go

Go Vet: ✅ Good
Tests: ✅ Passed

Fix locally:

go fmt ./...      # Format code
go vet ./...      # Check for issues
go test ./...     # Run tests

⚛️ Frontend Checks

Build & Type Check: ✅ Success

Fix locally:

cd web
npm run build  # Test build (includes type checking)

---

📖 Resources

• Contributing Guidelines
• Migration Guide

Questions? Feel free to ask in the comments! 🙏

---

These checks are advisory and won't block your PR from being merged. This comment is automatically generated from pr-checks-run.yml.

[github-actions]

🤖 Advisory Check Results

These are advisory checks to help improve code quality. They won't block your PR from being merged.

📋 PR Information

Title Format: ✅ Good - Follows Conventional Commits
PR Size: 🟢 Small (28 lines: +24 -4)

🔧 Backend Checks

Go Formatting: ⚠️ Needs formatting

Files needing formatting

api/errors.go
api/handler_wallet.go
cmd/e2e_builder_fee/main.go
market/types.go
mcp/config.go
mcp/context_guard_test.go
mcp/options.go
mcp/payment/claw402.go
mcp/request.go
mcp/request_builder.go

Go Vet: ✅ Good
Tests: ✅ Passed

Fix locally:

go fmt ./...      # Format code
go vet ./...      # Check for issues
go test ./...     # Run tests

⚛️ Frontend Checks

Build & Type Check: ✅ Success

Fix locally:

cd web
npm run build  # Test build (includes type checking)

---

📖 Resources

• Contributing Guidelines
• Migration Guide

Questions? Feel free to ask in the comments! 🙏

---

These checks are advisory and won't block your PR from being merged. This comment is automatically generated from pr-checks-run.yml.

[github-actions]

🤖 Advisory Check Results

These are advisory checks to help improve code quality. They won't block your PR from being merged.

📋 PR Information

Title Format: ✅ Good - Follows Conventional Commits
PR Size: 🟢 Small (28 lines: +24 -4)

🔧 Backend Checks

Go Formatting: ⚠️ Needs formatting

Files needing formatting

api/errors.go
api/handler_wallet.go
cmd/e2e_builder_fee/main.go
market/types.go
mcp/config.go
mcp/context_guard_test.go
mcp/options.go
mcp/payment/claw402.go
mcp/request.go
mcp/request_builder.go

Go Vet: ✅ Good
Tests: ✅ Passed

Fix locally:

go fmt ./...      # Format code
go vet ./...      # Check for issues
go test ./...     # Run tests

⚛️ Frontend Checks

Build & Type Check: ✅ Success

Fix locally:

cd web
npm run build  # Test build (includes type checking)

---

📖 Resources

• Contributing Guidelines
• Migration Guide

Questions? Feel free to ask in the comments! 🙏

---

These checks are advisory and won't block your PR from being merged. This comment is automatically generated from pr-checks-run.yml.

[github-actions]

🤖 Advisory Check Results

These are advisory checks to help improve code quality. They won't block your PR from being merged.

📋 PR Information

Title Format: ✅ Good - Follows Conventional Commits
PR Size: 🟢 Small (4 lines: +2 -2)

🔧 Backend Checks

Go Formatting: ⚠️ Needs formatting

Files needing formatting

api/errors.go
api/handler_wallet.go
cmd/e2e_builder_fee/main.go
market/types.go
mcp/config.go
mcp/context_guard_test.go
mcp/options.go
mcp/request.go
mcp/request_builder.go
provider/hyperliquid/kline.go

Go Vet: ✅ Good
Tests: ✅ Passed

Fix locally:

go fmt ./...      # Format code
go vet ./...      # Check for issues
go test ./...     # Run tests

⚛️ Frontend Checks

Build & Type Check: ✅ Success

Fix locally:

cd web
npm run build  # Test build (includes type checking)

---

📖 Resources

• Contributing Guidelines
• Migration Guide

Questions? Feel free to ask in the comments! 🙏

---

These checks are advisory and won't block your PR from being merged. This comment is automatically generated from pr-checks-run.yml.