Add Cohere provider (native streaming + tool use)

[quangdang46]

Add Cohere provider (native streaming + tool use)

Summary

Add a first-class Cohere provider with native streaming and tool calling. pi_agent_rust ships this as one of its 10 native providers; jcode does not currently support Cohere at all.

Reference: pi_agent_rust src/providers/cohere.rs and the provider list.

Why

• Cohere's Command-R family is competitive on tool-heavy workloads and is one of the few providers explicitly tuned for RAG + tool use, which lines up with jcode's memory + tool design.
• Adding a native Cohere path (vs forcing users through an OpenAI-compatible shim) lets jcode use Cohere's idiomatic tool format and streaming chunk schema, avoiding the schema-coercion bugs that hit Gemini ([Upstream PR #256] fix(server): eliminate multi-session protocol corruption #173, [Upstream #218] Jcode crashed back to terminal prompt during tool-heavy workflow session #162).

Current state in jcode

• src/provider/ lists Anthropic, OpenAI, Gemini, Bedrock, etc. No cohere.rs.
• --provider CLI doc string in src/cli/args.rs does not list cohere.
• No COHERE_API_KEY detection in src/cli/login/ flows.

Implementation checklist

1. Provider implementation

• Add src/provider/cohere.rs implementing the Provider trait:
  • Auth: Bearer $COHERE_API_KEY.
  • Endpoint: https://api.cohere.com/v2/chat (or v2/chat-stream).
  • Streaming: parse Cohere's event-stream chunks (event: ... + data: ...).
  • Tool-call format: map jcode ToolCall { name, args } to Cohere's parameters block; map results back from tool_results.
  • Reasoning support: surface tool_plan if present as a thinking block.
• Add Cohere to src/provider/mod.rs registry and the ProviderChoice enum.

2. Models

• Register at least: command-r-08-2024, command-r-plus-08-2024, command-a-03-2025. Context windows: 128k for r/r+ and 256k for a. Pull these into src/provider_catalog.rs.
• Document the canonical list and let users discover with jcode model list --provider cohere.

3. Auth + login

• Detect COHERE_API_KEY env var.
• Add jcode login --provider cohere flow: prompt for API key (with --api-key/--api-key-stdin), store via the standard auth.json mechanism.
• Add Cohere to auth-test covered providers.

4. CLI surface

• Update --provider doc string in src/cli/args.rs to include cohere.
• Update README.md provider list.

5. Error handling

• Map common error responses to typed errors: 401 → unauthenticated (surface in auth-test), 429 → rate-limit (apply existing retry/backoff), 400 with invalid_argument → log + redacted payload preview.

6. Telemetry

• Reuse the existing provider telemetry hooks so usage/cost are tracked.

Testing

Unit

• Streaming parser tests against fixture event streams from Cohere docs.
• Tool-call round-trip: jcode tool spec → Cohere request body → mocked response → parsed tool call → result delivered back.
• Auth-test "no key" path exits with an actionable error.

Live test (gated)

• Add live_tests::test_cohere behind JCODE_LIVE=1. Asserts a known short response with one tool call.

Manual

• jcode login --provider cohere, then jcode -m command-r-plus run "List files in src/" and verify a working tool call.

Acceptance criteria

• jcode --provider cohere -m command-r-plus run "..." works.
• Streaming, tool-call, and reasoning blocks all render in the TUI.
• jcode auth-test --provider cohere returns a clean OK.
• cargo test cohere passes; cargo clippy --all-targets -- -D warnings clean.

References

• pi_agent_rust: Cohere provider source.
• Cohere v2 chat docs.

---

Implementation notes addendum (Devin gap-analysis pass, 2026-05-21)

Verified jcode code paths

• Provider scaffolding mirrors existing native providers in src/provider/ (e.g. src/provider/anthropic.rs, src/provider/openai.rs, src/provider/claude.rs, src/provider/gemini.rs).
• Provider catalog: src/provider_catalog.rs + crates/jcode-provider-metadata/src/catalog.rs.
• Streaming SSE parser: src/transport/ (reuse, do not write a new one).
• Per-provider tests pattern: tests/integration/<provider>.rs (offline fixtures via recorded JSON streams).

Cohere API specifics

• API: Cohere v2 chat/completions (https://api.cohere.com/v2/chat).
• Auth: Authorization: Bearer <api-key> from env CO_API_KEY (also accept COHERE_API_KEY for compat).
• Streaming: Server-Sent Events; event types include message-start, content-delta, tool-call-start, tool-call-delta, tool-call-end, message-end. Map to jcode's internal stream events.
• Tool use: Cohere has native tools array in the request; pass jcode's tool schemas through unchanged.
• Models to register at launch: command-r-plus, command-r, command-r-08-2024, command-a-03-2025 (most recent at issue-time). Source via https://api.cohere.com/v1/models.

Acceptance criteria

• jcode --provider cohere --model command-r-plus "..." works end-to-end.
• Streaming output renders incrementally.
• Tool calls work (test with read).
• jcode --list-providers includes Cohere.
• Token/cost accounting populated.
• Tests cover one streamed response and one tool-call round-trip via offline fixtures.

Cross-references

• Add GitLab Duo provider (subscription-backed coding model) #19 GitLab Duo — sibling provider issue.

Reference

• pi_agent_rust: src/providers/cohere.rs.
• Cohere docs: https://docs.cohere.com/docs/streaming