Add DeepSeek as a first-class model provider

crates/adapter-smith/src/agent.rs

@@ -69,6 +69,9 @@ const APPROVAL_HISTORY_LIMIT: usize = 20;
 /// Purely a function of observed progress — model- and provider-agnostic.
 const NONPRODUCTIVE_STREAK_LIMIT: usize = 4;
 const GROK_BASE_URL: &str = "https://api.x.ai/v1";
+/// DeepSeek's OpenAI-compatible surface. Served by the same
+/// `provider::openai` client as Grok — the wire format is chat completions.
+const DEEPSEEK_BASE_URL: &str = "https://api.deepseek.com/v1";
 
 fn record_approval_history(
     history: &mut VecDeque<ApprovalHistoryEntry>,
@@ -1577,6 +1580,7 @@ impl ResolvedModel {
             provider::routing::Provider::Meta => "meta",
             provider::routing::Provider::Ollama => "ollama",
             provider::routing::Provider::Grok => "grok",
+            provider::routing::Provider::DeepSeek => "deepseek",
             provider::routing::Provider::GrokOauth => "grok-oauth",
             provider::routing::Provider::CodexOauth => "codex-oauth",
             provider::routing::Provider::ClaudeOauth => "claude-oauth",
@@ -1611,7 +1615,8 @@ impl ResolvedModel {
 ///   4. OPENAI_API_KEY set → `gpt-5`.
 ///   5. GEMINI_API_KEY (or GOOGLE_API_KEY) set → `gemini-2.5-pro`.
 ///   6. META_API_KEY (or MODEL_API_KEY) set → `muse-spark-1.1`.
-///   7. none of the above → an error (spec 0069). Earlier versions fell
+///   7. DEEPSEEK_API_KEY set → `deepseek-v4-pro`.
+///   8. none of the above → an error (spec 0069). Earlier versions fell
 ///      through to `ollama:llama3.1` here unconditionally, so a zero-config
 ///      machine with no Ollama server running got a session that looked
 ///      healthy and then died mid-turn with a raw transport error instead
@@ -1637,7 +1642,7 @@ pub fn resolve_model(params: &SessionStartParams) -> Result<ResolvedModel> {
     resolve_model_from_spec(&spec_str)
 }
 
-/// The auto-detect ladder's direct-API-key rungs (steps 3-5 above), used
+/// The auto-detect ladder's direct-API-key rungs (steps 3-7 above), used
 /// when neither `--model` nor `CONSTRUCT_SMITH_MODEL` is set. Returns an
 /// error rather than silently picking a provider that isn't configured.
 fn default_auto_detect_spec() -> Result<String> {
@@ -1653,10 +1658,16 @@ fn default_auto_detect_spec() -> Result<String> {
     if std::env::var("META_API_KEY").is_ok() || std::env::var("MODEL_API_KEY").is_ok() {
         return Ok("meta:muse-spark-1.1".to_string());
     }
+    // Last rung: a machine whose only credential is DeepSeek's still gets a
+    // working session instead of the curated error. Ordered after the others
+    // so no machine that already resolved changes provider (spec 0071).
+    if std::env::var("DEEPSEEK_API_KEY").is_ok() {
+        return Ok("deepseek:deepseek-v4-pro".to_string());
+    }
     anyhow::bail!(
         "no auto-detected smith credential (ANTHROPIC_API_KEY, OPENAI_API_KEY, or \
-         GEMINI_API_KEY/GOOGLE_API_KEY, or META_API_KEY/MODEL_API_KEY) and no \
-         CONSTRUCT_SMITH_MODEL pin set"
+         GEMINI_API_KEY/GOOGLE_API_KEY, or META_API_KEY/MODEL_API_KEY, or \
+         DEEPSEEK_API_KEY) and no CONSTRUCT_SMITH_MODEL pin set"
     )
 }
 
@@ -1687,6 +1698,10 @@ pub fn resolve_model_from_spec(spec_str: &str) -> Result<ResolvedModel> {
             Some(GROK_BASE_URL.to_string()),
             grok_api_key()?,
         )?),
+        provider::routing::Provider::DeepSeek => Box::new(provider::openai::OpenAi::with_config(
+            Some(DEEPSEEK_BASE_URL.to_string()),
+            deepseek_api_key()?,
+        )?),
         provider::routing::Provider::GrokOauth => Box::new(provider::openai::OpenAi::with_config(
             Some(GROK_BASE_URL.to_string()),
             grok_oauth_token()?,
@@ -1745,6 +1760,7 @@ fn build_profile_model(
         "meta" => provider::routing::Provider::Meta,
         "ollama" => provider::routing::Provider::Ollama,
         "grok" => provider::routing::Provider::Grok,
+        "deepseek" => provider::routing::Provider::DeepSeek,
         "codex-oauth" | "claude-oauth" | "claude-code-oauth" | "grok-oauth" | "kimi-oauth" => anyhow::bail!(
             "profile `{name}`: provider `{}` is OAuth-backed and has no \
              configurable endpoint — use the `{}:` model prefix directly",
@@ -1753,7 +1769,7 @@ fn build_profile_model(
         ),
         other => anyhow::bail!(
             "profile `{name}`: unknown provider `{other}` \
-             (expected openai | anthropic | gemini | meta | ollama | grok)"
+             (expected openai | anthropic | gemini | meta | ollama | grok | deepseek)"
         ),
     };
 
@@ -1793,6 +1809,10 @@ fn build_profile_model(
             base_url.or_else(|| Some(GROK_BASE_URL.to_string())),
             profile_api_key(profile, name, &["GROK_API_KEY", "XAI_API_KEY"])?,
         )?),
+        provider::routing::Provider::DeepSeek => Box::new(provider::openai::OpenAi::with_config(
+            base_url.or_else(|| Some(DEEPSEEK_BASE_URL.to_string())),
+            profile_api_key(profile, name, &["DEEPSEEK_API_KEY"])?,
+        )?),
         // codex-oauth / claude-oauth / grok-oauth rejected above.
         _ => unreachable!("oauth providers rejected above"),
     };
@@ -1839,6 +1859,11 @@ fn grok_api_key() -> Result<String> {
         .map_err(|_| anyhow::anyhow!("grok provider requires GROK_API_KEY or XAI_API_KEY"))
 }
 
+fn deepseek_api_key() -> Result<String> {
+    std::env::var("DEEPSEEK_API_KEY")
+        .map_err(|_| anyhow::anyhow!("deepseek provider requires DEEPSEEK_API_KEY"))
+}
+
 fn grok_auth_path() -> Result<PathBuf> {
     if let Ok(home) = std::env::var("GROK_HOME") {
         if !home.trim().is_empty() {
@@ -2298,6 +2323,7 @@ mod tests {
             "GOOGLE_API_KEY",
             "META_API_KEY",
             "MODEL_API_KEY",
+            "DEEPSEEK_API_KEY",
         ];
         let saved: Vec<Option<String>> = vars.iter().map(|v| env::var(v).ok()).collect();
         for v in vars {
@@ -2317,7 +2343,7 @@ mod tests {
     }
 
     #[test]
-    fn default_auto_detect_spec_precedence_anthropic_openai_gemini_then_meta() {
+    fn default_auto_detect_spec_precedence_anthropic_openai_gemini_meta_then_deepseek() {
         let _lock = MODEL_ENV_LOCK.lock().unwrap();
         let vars = [
             "ANTHROPIC_API_KEY",
@@ -2326,12 +2352,17 @@ mod tests {
             "GOOGLE_API_KEY",
             "META_API_KEY",
             "MODEL_API_KEY",
+            "DEEPSEEK_API_KEY",
         ];
         let saved: Vec<Option<String>> = vars.iter().map(|v| env::var(v).ok()).collect();
         for v in vars {
             env::remove_var(v);
         }
 
+        // DeepSeek is the last rung: it resolves when it is the only key, and
+        // yields to every other direct-API credential.
+        env::set_var("DEEPSEEK_API_KEY", "x");
+        let deepseek_only = default_auto_detect_spec().expect("deepseek");
         env::set_var("MODEL_API_KEY", "x");
         let meta_only = default_auto_detect_spec().expect("meta");
         env::set_var("GEMINI_API_KEY", "x");
@@ -2347,6 +2378,7 @@ mod tests {
                 None => env::remove_var(v),
             }
         }
+        assert_eq!(deepseek_only, "deepseek:deepseek-v4-pro");
         assert_eq!(meta_only, "meta:muse-spark-1.1");
         assert_eq!(gemini_over_meta, "gemini:gemini-2.5-pro");
         assert_eq!(openai_over_gemini, "openai:gpt-5");

crates/adapter-smith/src/context.rs

@@ -39,6 +39,11 @@ pub fn context_window_tokens(provider: &str, model: &str) -> usize {
         // cloud endpoint (order-of-magnitude in the same class as recent
         // OpenAI models); this is a safe conservative starting value.
         ("grok", _) => 100_000,
+        // DeepSeek's V4 line (pro and flash) both advertise a 1M-token
+        // context window. Without an entry here the `_` arm would cap the
+        // session at 8K and compact almost immediately on a model that can
+        // hold the whole conversation.
+        ("deepseek", _) => 1_000_000,
         // ChatGPT-subscription Codex backend. Same gpt-5* family,
         // same advertised context window as the platform API — the
         // billing pipe is what differs, not the model. Starting
@@ -381,6 +386,22 @@ mod tests {
         }
     }
 
+    /// A provider with no entry falls to the 8K default, which would compact
+    /// a 1M-context model almost immediately. Regression guard for the
+    /// DeepSeek arm specifically, since the fallthrough is silent.
+    #[test]
+    fn deepseek_gets_its_real_context_window_not_the_default() {
+        assert_eq!(context_window_tokens("deepseek", "deepseek-v4-pro"), 1_000_000);
+        assert_eq!(
+            context_window_tokens("deepseek", "deepseek-v4-flash"),
+            1_000_000
+        );
+        assert!(
+            context_window_tokens("deepseek", "some-future-model") > 8_000,
+            "an unrecognized DeepSeek model must not fall to the generic default"
+        );
+    }
+
     #[test]
     fn no_prune_under_budget() {
         let mut ms = vec![user("hi"), asst("hello")];

crates/adapter-smith/src/lib.rs

@@ -146,6 +146,8 @@ fn model_startup_error_message(params: &SessionStartParams, error: &str) -> Stri
         msg.push_str(
             "\n\nAction: set `GEMINI_API_KEY` or `GOOGLE_API_KEY`, or switch smith to another model.",
         );
+    } else if lower.contains("deepseek_api_key") {
+        msg.push_str("\n\nAction: set `DEEPSEEK_API_KEY` or switch smith to another model.");
     } else if lower.contains("meta_api_key") || lower.contains("model_api_key") {
         msg.push_str(
             "\n\nAction: set `META_API_KEY` or `MODEL_API_KEY`, or switch smith to another model.",
@@ -162,7 +164,7 @@ fn model_startup_error_message(params: &SessionStartParams, error: &str) -> Stri
     msg.push_str(
         "\n\nsmith needs one of: `CONSTRUCT_SMITH_MODEL`, `ANTHROPIC_API_KEY`, \
          `OPENAI_API_KEY`, `GEMINI_API_KEY`, `META_API_KEY`/`MODEL_API_KEY`, `GROK_API_KEY`/`XAI_API_KEY`, \
-         a valid Grok OAuth login, or a local Ollama. Run `/configure` in the construct TUI \
+         `DEEPSEEK_API_KEY`, a valid Grok OAuth login, or a local Ollama. Run `/configure` in the construct TUI \
          (or `M-x configure`) to check status and pick one.",
     );
     msg

crates/adapter-smith/src/provider/routing.rs

@@ -1,11 +1,13 @@
 //! Translate a model spec string into a (provider, bare model name).
 //!
 //! Explicit prefixes (`openai:`, `anthropic:`, `gemini:`, `meta:`, `ollama:`,
-//! `grok:`, `grok-oauth:`, `codex-oauth:`, `claude-oauth:`, `claude-code-oauth:`) always win.
+//! `grok:`, `deepseek:`, `grok-oauth:`, `codex-oauth:`, `claude-oauth:`,
+//! `claude-code-oauth:`) always win.
 //! Otherwise we sniff the bare name:
 //!   - starts with `gpt-` or `o[1-5]` → OpenAI
 //!   - starts with `claude-` → Anthropic
 //!   - starts with `gemini-` → Gemini
+//!   - starts with `deepseek` → DeepSeek
 //!   - anything else → Ollama (local fallback)
 //!
 //! Returning an enum keeps the dispatch table small and testable.
@@ -31,6 +33,9 @@ pub enum Provider {
     Ollama,
     /// xAI Grok API surface.
     Grok,
+    /// DeepSeek platform API surface. OpenAI-compatible chat completions at
+    /// `api.deepseek.com`, billed against a DeepSeek API key.
+    DeepSeek,
     /// OAuth-backed Grok access path.
     GrokOauth,
     /// OAuth-backed Codex backend; reads `~/.codex/auth.json`, bills
@@ -91,6 +96,12 @@ pub fn parse_model_spec(s: &str) -> Result<ModelSpec, String> {
             model: rest.to_string(),
         });
     }
+    if let Some(rest) = s.strip_prefix("deepseek:") {
+        return Ok(ModelSpec {
+            provider: Provider::DeepSeek,
+            model: rest.to_string(),
+        });
+    }
     if let Some(rest) = s.strip_prefix("grok-oauth:") {
         return Ok(ModelSpec {
             provider: Provider::GrokOauth,
@@ -129,6 +140,7 @@ pub fn parse_model_spec(s: &str) -> Result<ModelSpec, String> {
                     | "meta"
                     | "ollama"
                     | "grok"
+                    | "deepseek"
                     | "grok-oauth"
                     | "codex-oauth"
                     | "claude-oauth"
@@ -138,7 +150,7 @@ pub fn parse_model_spec(s: &str) -> Result<ModelSpec, String> {
         {
             return Err(format!(
                 "unknown provider prefix `{prefix}:` (expected one of \
-                 openai:, anthropic:, gemini:, meta:, ollama:, grok:, grok-oauth:, codex-oauth:, claude-oauth:, kimi-oauth:)"
+                 openai:, anthropic:, gemini:, meta:, ollama:, grok:, deepseek:, grok-oauth:, codex-oauth:, claude-oauth:, kimi-oauth:)"
             ));
         }
     }
@@ -150,6 +162,8 @@ pub fn parse_model_spec(s: &str) -> Result<ModelSpec, String> {
         Provider::Gemini
     } else if s.starts_with("grok") {
         Provider::Grok
+    } else if s.starts_with("deepseek") {
+        Provider::DeepSeek
     } else {
         Provider::Ollama
     };
@@ -310,6 +324,35 @@ mod tests {
         assert_eq!(s.model, "grok-2-1212");
     }
 
+    #[test]
+    fn deepseek_prefix_is_recognized() {
+        let s = parse("deepseek:deepseek-v4-pro");
+        assert_eq!(s.provider, Provider::DeepSeek);
+        assert_eq!(s.model, "deepseek-v4-pro");
+    }
+
+    /// Every model DeepSeek serves is named `deepseek-*`, so the bare name is
+    /// unambiguous — unlike `claude-*`/`gpt-*`, no other vendor claims it.
+    #[test]
+    fn bare_deepseek_model_routes_to_deepseek() {
+        assert_eq!(parse("deepseek-v4-pro").provider, Provider::DeepSeek);
+        assert_eq!(parse("deepseek-v4-flash").provider, Provider::DeepSeek);
+        // The retired `deepseek-chat` / `deepseek-reasoner` ids are still
+        // accepted by the API (it maps them onto a current model), so they
+        // must keep reaching DeepSeek rather than falling through to Ollama.
+        assert_eq!(parse("deepseek-chat").provider, Provider::DeepSeek);
+        assert_eq!(parse("deepseek-reasoner").provider, Provider::DeepSeek);
+    }
+
+    /// A DeepSeek model served by some other endpoint (an OpenAI-compatible
+    /// reseller, a local copy) is still reachable — the bare-name sniff is a
+    /// default, and an explicit prefix or `@profile` overrides it.
+    #[test]
+    fn explicit_prefix_beats_deepseek_sniff() {
+        assert_eq!(parse("ollama:deepseek-v4-flash").provider, Provider::Ollama);
+        assert_eq!(parse("openai:deepseek-v4-pro").provider, Provider::OpenAI);
+    }
+
     #[test]
     fn claude_oauth_prefixes_are_recognized() {
         let s = parse("claude-oauth:sonnet");

crates/adapter-smith/src/title_mode.rs

@@ -55,6 +55,10 @@ pub(crate) fn pick_default_spec_str() -> Result<String> {
     if std::env::var("META_API_KEY").is_ok() || std::env::var("MODEL_API_KEY").is_ok() {
         return Ok("meta:muse-spark-1.1".to_string());
     }
+    if std::env::var("DEEPSEEK_API_KEY").is_ok() {
+        // Flash is the cheap tier — titles never need the pro model.
+        return Ok("deepseek:deepseek-v4-flash".to_string());
+    }
     Err(anyhow!(
         "no auto-detected smith credential and no CONSTRUCT_SMITH_MODEL pin set; skipping auto-title"
     ))
@@ -73,6 +77,11 @@ pub(crate) fn provider_for(p: Provider) -> Result<Box<dyn LlmProvider>> {
                 .or_else(|_| std::env::var("XAI_API_KEY"))
                 .map_err(|_| anyhow!("grok requires GROK_API_KEY or XAI_API_KEY"))?,
         )?),
+        Provider::DeepSeek => Box::new(provider::openai::OpenAi::with_config(
+            Some("https://api.deepseek.com/v1".to_string()),
+            std::env::var("DEEPSEEK_API_KEY")
+                .map_err(|_| anyhow!("deepseek requires DEEPSEEK_API_KEY"))?,
+        )?),
         // Title generation always uses one of the key providers above; the
         // user never picks OAuth providers for title-gen since the
         // selection comes from `pick_default_spec_str` which only

crates/cli/src/app/configure.rs

@@ -111,6 +111,9 @@ pub fn smith_method_guidance(id: &str) -> &'static str {
             "export GROK_API_KEY (or XAI_API_KEY) in the shell that starts the daemon, then \
              restart the daemon"
         }
+        "deepseek_api_key" => {
+            "export DEEPSEEK_API_KEY in the shell that starts the daemon, then restart the daemon"
+        }
         "claude_subscription" => {
             "run `claude` and log in with your Claude subscription first (creates \
              ~/.claude/.credentials.json), as the user the daemon runs as, then restart the daemon"