feat(config): add context_window field to decouple input/output token limits

Adds a new `context_window` field to AgentDefaults that separates the context
window (used for summarization threshold calculation) from max_tokens (used
for output length limit).

Changes:
- pkg/config/config.go: Add ContextWindow field with JSON/env support
- pkg/config/defaults.go: Set default to 131072 (128K)
- pkg/agent/instance.go: Use context_window with fallback to max_tokens
- config/config.example.json: Add example configuration
- README.md, docs/docker.md, docs/providers.md: Update documentation

Backward compatibility: If context_window is not set, it defaults to max_tokens.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -274,6 +274,7 @@ picoclaw onboard
       "workspace": "~/.picoclaw/workspace",
       "model_name": "gpt-5.4",
       "max_tokens": 8192,
+      "context_window": 131072,
       "temperature": 0.7,
       "max_tool_iterations": 20
     }
@@ -1019,6 +1020,7 @@ picoclaw onboard
       "workspace": "~/.picoclaw/workspace",
       "model_name": "gpt-5.4",
       "max_tokens": 8192,
+      "context_window": 131072,
       "temperature": 0.7,
       "max_tool_iterations": 20
     }

config/config.example.json

@@ -5,6 +5,7 @@
       "restrict_to_workspace": true,
       "model_name": "gpt-5.4",
       "max_tokens": 8192,
+      "context_window": 131072,
       "temperature": 0.7,
       "max_tool_iterations": 20,
       "summarize_message_threshold": 20,

docs/docker.md

@@ -84,6 +84,7 @@ picoclaw onboard
       "workspace": "~/.picoclaw/workspace",
       "model_name": "gpt-5.4",
       "max_tokens": 8192,
+      "context_window": 131072,
       "temperature": 0.7,
       "max_tool_iterations": 20
     }

docs/providers.md

@@ -95,7 +95,9 @@ This design also enables **multi-agent support** with flexible provider selectio
   ],
   "agents": {
     "defaults": {
-      "model_name": "gpt-5.4"
+      "model_name": "gpt-5.4",
+      "max_tokens": 8192,
+      "context_window": 131072
     }
   }
 }

pkg/agent/instance.go

@@ -130,6 +130,12 @@ func NewAgentInstance(
 		maxTokens = 8192
 	}
 
+	// Resolve context window: use context_window if set, otherwise fall back to max_tokens
+	contextWindow := defaults.ContextWindow
+	if contextWindow == 0 {
+		contextWindow = maxTokens
+	}
+
 	temperature := 0.7
 	if defaults.Temperature != nil {
 		temperature = *defaults.Temperature
@@ -182,7 +188,7 @@ func NewAgentInstance(
 		MaxTokens:                 maxTokens,
 		Temperature:               temperature,
 		ThinkingLevel:             thinkingLevel,
-		ContextWindow:             maxTokens,
+		ContextWindow:             contextWindow,
 		SummarizeMessageThreshold: summarizeMessageThreshold,
 		SummarizeTokenPercent:     summarizeTokenPercent,
 		Provider:                  provider,

pkg/config/config.go

@@ -238,6 +238,7 @@ type AgentDefaults struct {
 	ImageModel                string             `json:"image_model,omitempty"           env:"PICOCLAW_AGENTS_DEFAULTS_IMAGE_MODEL"`
 	ImageModelFallbacks       []string           `json:"image_model_fallbacks,omitempty"`
 	MaxTokens                 int                `json:"max_tokens"                      env:"PICOCLAW_AGENTS_DEFAULTS_MAX_TOKENS"`
+	ContextWindow             int                `json:"context_window"                 env:"PICOCLAW_AGENTS_DEFAULTS_CONTEXT_WINDOW"`
 	Temperature               *float64           `json:"temperature,omitempty"           env:"PICOCLAW_AGENTS_DEFAULTS_TEMPERATURE"`
 	MaxToolIterations         int                `json:"max_tool_iterations"             env:"PICOCLAW_AGENTS_DEFAULTS_MAX_TOOL_ITERATIONS"`
 	SummarizeMessageThreshold int                `json:"summarize_message_threshold"     env:"PICOCLAW_AGENTS_DEFAULTS_SUMMARIZE_MESSAGE_THRESHOLD"`

pkg/config/defaults.go

@@ -31,6 +31,7 @@ func DefaultConfig() *Config {
 				Provider:                  "",
 				Model:                     "",
 				MaxTokens:                 32768,
+				ContextWindow:             131072,
 				Temperature:               nil, // nil means use provider default
 				MaxToolIterations:         50,
 				SummarizeMessageThreshold: 20,