Summary

• Problem: byterover-cli is missing DeepSeek (one of four user-requested providers) and lacks a way to route through Z.AI's Coding Plan subscription endpoint. Separately, DeepSeek reasoning models were mapped to a think-tags parser that never matched the API's actual reasoning_content field — reasoning output was silently dropped.
• Why it matters: the four user-requested providers (DeepSeek, MiniMax, Moonshot/Kimi, Z.AI); correct billing for Z.AI Coding Plan subscribers (standard endpoint hits pay-per-token quota); DeepSeek users can finally see reasoning output instead of empty thinking blocks.
• What changed:
  • New deepseek provider via @ai-sdk/openai-compatible against https://api.deepseek.com/v1 (env DEEPSEEK_API_KEY).
  • New glm-coding-plan provider as a separate ID alongside the existing glm, pointing at https://api.z.ai/api/coding/paas/v4, reusing ZHIPU_API_KEY.
  • Capability fix: deepseek-r1 / deepseek-reasoner now correctly map to reasoningFormat: 'native-field' with reasoningField: 'reasoning_content'.
  • DeepSeek SVG icon (Wikimedia Commons, MIT-licensed, whale-only path with cropped viewBox); GLM Coding Plan reuses the existing zai icon.
  • README provider table bumped 18 → 20.
• What did NOT change (scope boundary): MiniMax, Moonshot/Kimi, and standard glm were already wired and untouched. No kimi-coding-plan provider, and Moonshot's coding-plan tier uses the same api.moonshot.ai/v1 endpoint as the standard provider. zhipuai-coding-plan (mainland-CN), minimax-coding-plan (Anthropic-compatible), and full models.dev catalog adoption are deferred per plan/llm-providers/DESIGN.md D3/D4.

Type of change

• Bug fix
• New feature
• Refactor (no behavior change)
• Documentation
• Test
• Chore (build, dependencies, CI)

Scope (select all touched areas)

• TUI / REPL
• Agent / Tools
• LLM Providers
• Server / Daemon
• Shared (constants, types, transport events)
• CLI Commands (oclif)
• Hub / Connectors
• Cloud Sync
• CI/CD / Infra

Linked issues

• Closes #N/A
• Related #N/A

Root cause (bug fixes only)

• Root cause: getModelCapabilities() in src/agent/infra/llm/model-capabilities.ts mapped deepseek-r1 / deepseek-reasoner to reasoningFormat: 'think-tags'. DeepSeek's OpenAI-compatible API does not emit <think>...</think> markers — it streams reasoning in a native reasoning_content field. The think-tag scanner never matched, so reasoning content was effectively dropped on the floor.
• Why this was not caught earlier: DeepSeek had no provider-registry entry, so it was never reachable through brv providers connect and never exercised end-to-end. The capability rule sat in a code path that no integration test could trigger. The fix is forced by adding the provider; this PR closes the loop in one go.

Test plan

• Coverage added:
  • Unit test
  • Integration test
  • Manual verification only
• Test file(s):
  • test/unit/agent/llm/model-capabilities.test.ts (new) — 3 assertions for the capability fix
  • test/unit/agent/llm/providers/deepseek.test.ts (new) — 6 assertions for provider-module shape
  • test/unit/agent/llm/providers/glm-coding-plan.test.ts (new) — 7 assertions for provider-module shape
  • test/unit/core/domain/entities/provider-registry.test.ts (extended) — 13 new assertions (6 DeepSeek + 7 GLM Coding Plan)
• Key scenario(s) covered:
  • Both new providers registered with correct base URL, env var, default model
  • deepseek-reasoner and deepseek-r1 resolve to native-field / reasoning_content; deepseek-chat reports no reasoning
  • glm-coding-plan coexists with glm (regression check that getProviderById('glm') still resolves and the two have distinct base URLs)
  • providerRequiresApiKey('deepseek') and providerRequiresApiKey('glm-coding-plan') both return true

User-visible changes

• New entries in brv providers connect picker: DeepSeek and GLM Coding Plan (Z.AI).
• DeepSeek reasoning models (deepseek-reasoner, deepseek-r1) now stream reasoning into the dedicated thinking block instead of silently dropping it.
• Z.AI Coding Plan subscribers can now route through the dedicated endpoint to consume subscription quota (previously only the standard pay-per-token endpoint was reachable).
• README provider table updated from 18 to 20 providers.

Evidence

• Failing test/log before + passing after

TDD sequence (full output in commit history):

# Before implementation — 13 assertions red for the right reason
$ npx mocha "test/unit/core/domain/entities/provider-registry.test.ts" \
            "test/unit/agent/llm/model-capabilities.test.ts" \
            "test/unit/agent/llm/providers/deepseek.test.ts"
  6) Provider Registry > DeepSeek provider > should be registered:
     AssertionError: expected undefined not to be undefined
  ...
  22 passing, 13 failing

# After implementation — full suite green
$ npm test
  7316 passing (19s)
  16 pending

Targeted run after Phase 2 (DeepSeek + GLM Coding Plan):

$ npx mocha "test/unit/core/domain/entities/provider-registry.test.ts" \
            "test/unit/agent/llm/providers/glm-coding-plan.test.ts" \
            "test/unit/agent/llm/providers/deepseek.test.ts" \
            "test/unit/agent/llm/model-capabilities.test.ts"
  51 passing (9ms)

Checklist

• Tests added or updated and passing (npm test — 7316 passing)
• Lint passes (npm run lint — 0 errors)
• Type check passes (npm run typecheck — root + webui clean)
• Build succeeds (npm run build)
• Commits follow Conventional Commits format (feat: prefix)
• Documentation updated (README provider table)
• No breaking changes (capability fix is a behavior change, but the old code path never matched any real response — see Root cause above)
• Branch is up to date with main

Risks and mitigations

• Risk: the hardcoded model list for glm-coding-plan includes glm-5-turbo.
  • Mitigation: if the model 404s, drop it from the array in provider-model-fetcher-registry.ts. Smoke test with a subscription holder is documented as a follow-up in plan/llm-providers/IMPLEMENTATION.md §2.3.
• Risk: the DeepSeek capability fix changes parsed output for any user who already had deepseek-reasoner accessible via OpenRouter (or any other route that flows through getModelCapabilities).
  • Mitigation: the prior think-tags mapping never matched a real DeepSeek response, so users were not seeing reasoning anyway — this is a fix, not a regression. OpenRouter has its own capability detection path that is unaffected.
• Risk: standard glm users on the Z.AI Coding Plan subscription might not realize they need to switch to the new glm-coding-plan provider to consume their subscription quota.
  • Mitigation: distinct names in the picker (GLM (Z.AI) vs GLM Coding Plan (Z.AI)) and the description string call out the subscription. README table makes both explicit.