fix(agent): decouple context_window from max_tokens by repfigit · Pull Request #556 · sipeed/picoclaw

repfigit · 2026-02-20T22:57:50Z

Summary

Add configurable context_window field to AgentDefaults with a 128K default
Fix bug where ContextWindow was incorrectly set to MaxTokens (typically 8192), causing overly aggressive context trimming
Add .gitattributes to enforce LF line endings

Test plan

go build ./...
go test ./pkg/config/... ./pkg/agent/...
Test with a config that omits context_window — should default to 128K
Test with a config that sets context_window: 64000 — should use 64K

🤖 Generated with Claude Code

Copilot

Pull request overview

This PR fixes a critical bug where the agent's context window was incorrectly set to the max tokens value (typically 8192), causing premature context trimming. The fix decouples context_window from max_tokens by adding a dedicated configurable field with a sensible 128K default, aligning with modern LLM capabilities.

Changes:

Added ContextWindow field to AgentDefaults config struct with environment variable support
Fixed NewAgentInstance to use dedicated context window value (defaulting to 128K) instead of max tokens
Added .gitattributes to enforce LF line endings across the repository

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
pkg/config/config.go	Adds `ContextWindow` field to `AgentDefaults` struct with JSON and environment variable tags
pkg/agent/instance.go	Introduces context window initialization logic with 128K default and uses it instead of max tokens
.gitattributes	Enforces LF line endings for all text files to ensure consistency across platforms

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Copilot · 2026-02-20T23:01:04Z

pkg/config/config.go

 	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,omitempty" env:"PICOCLAW_AGENTS_DEFAULTS_CONTEXT_WINDOW"`


The ContextWindow field uses omitempty in its JSON tag, which is inconsistent with similar integer fields like MaxTokens (line 177) and MaxToolIterations (line 180) that don't use omitempty. For consistency and to match the existing pattern for integer configuration fields with defaults in AgentDefaults, consider removing omitempty from the JSON tag.

Suggested change

ContextWindow int `json:"context_window,omitempty" env:"PICOCLAW_AGENTS_DEFAULTS_CONTEXT_WINDOW"`

ContextWindow int `json:"context_window" env:"PICOCLAW_AGENTS_DEFAULTS_CONTEXT_WINDOW"`

Copilot · 2026-02-20T23:01:04Z

pkg/agent/instance.go

+	contextWindow := defaults.ContextWindow
+	if contextWindow == 0 {
+		contextWindow = 128000
+	}


The new ContextWindow field lacks test coverage. Similar fields like MaxTokens and Temperature have dedicated tests in instance_test.go (e.g., TestNewAgentInstance_UsesDefaultsTemperatureAndMaxTokens). Consider adding tests to verify:

ContextWindow uses the configured value when provided

ContextWindow defaults to 128000 when not configured (zero value)
This is important because ContextWindow affects critical behavior like context trimming in loop.go (lines 727 and 892).

Since picoclaw is intended to work on low-end machine, by default we should set a smaller value (better to keep 8192, the current value). Users with devices that have larger memory could set this value explicitly in the config file.

Please also update the README.md for this feature.

Let the users to set this value may not be convient, I think the better way is when running the onboard guidance, ask the user their preference for deploying corresponding devices.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Add configurable context_window field to AgentDefaults with a 128K default. Previously ContextWindow was incorrectly set to MaxTokens (typically 8192), causing overly aggressive context trimming. Co-Authored-By: Claude Opus 4.6 <[email protected]>

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

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Copilot · 2026-02-20T23:39:58Z

pkg/config/config.go

 	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"`


ContextWindow is added without omitempty, but DefaultConfig() (used by onboarding + SaveConfig) does not set this field yet. As a result, newly generated config files will likely include "context_window": 0, which conflicts with the stated 128K default and is confusing for users. Consider either setting ContextWindow to 128000 in DefaultConfig() (preferred if you want the default to be visible) or adding omitempty to this JSON tag so the field is omitted when unset.

@repfigit I didn't see the DefaultConfig changes.

xiaket · 2026-02-22T00:09:44Z

.gitattributes

Why do we need to change this file in a fix PR?

xiaket · 2026-02-22T00:11:15Z

pkg/agent/instance.go


+	contextWindow := defaults.ContextWindow
+	if contextWindow == 0 {
+		contextWindow = 128000


Please at the very least state your rationale here. I share the same concern that @zenixls2 has raised.

nikolasdehor

Good bug fix. Setting ContextWindow = maxTokens (typically 8192) is clearly wrong - the context window is the total input capacity, not the output token limit. This would cause premature summarization on models with large context windows.

The fix is clean: add a configurable ContextWindow field with a 128K default. The tests cover both the configured and default cases.

One suggestion: 128K is a reasonable default for modern models (GPT-4+, Claude, Gemini), but some smaller/local models have 4K-32K context windows. Users running Ollama with smaller models might not notice they need to configure this. Consider logging a debug message when using the 128K default, or documenting this in the config example.

The .gitattributes addition for LF line endings is fine but unrelated - consider separating it into its own PR for clean history. Not a blocker.

LGTM.

CLAassistant · 2026-03-05T15:08:39Z

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…and safe compression Separate context_window from max_tokens — they serve different purposes (input capacity vs output generation limit). The previous conflation caused premature summarization or missed compression triggers. Changes: - Add context_window field to AgentDefaults config (default: 4x max_tokens) - Extract boundary-safe truncation helpers (isSafeBoundary, findSafeBoundary) into context_budget.go — pure functions with no AgentLoop dependency - forceCompression: align split to safe boundary so tool-call sequences (assistant+ToolCalls → tool results) are never torn apart - summarizeSession: use findSafeBoundary instead of hardcoded keep-last-4 - estimateTokens: count ToolCalls arguments and ToolCallID metadata, not just Content — fixes systematic undercounting in tool-heavy sessions - Add proactive context budget check before LLM call in runAgentLoop, preventing 400 context-length errors instead of reacting to them - Add estimateToolDefsTokens for tool definition token cost Closes sipeed#556, closes sipeed#665 Ref sipeed#1439

Copilot AI review requested due to automatic review settings February 20, 2026 22:57

Copilot started reviewing on behalf of repfigit February 20, 2026 22:58 View session

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chore: add .gitattributes to enforce LF line endings

902c701

Co-Authored-By: Claude Opus 4.6 <[email protected]>

repfigit force-pushed the fix/context-window-default branch from 03a6b3a to 8afe597 Compare February 20, 2026 23:09

Copilot AI review requested due to automatic review settings February 20, 2026 23:36

repfigit force-pushed the fix/context-window-default branch from 8afe597 to 06ee821 Compare February 20, 2026 23:36

Copilot started reviewing on behalf of repfigit February 20, 2026 23:37 View session

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xiaket reviewed Feb 22, 2026

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Why do we need to change this file in a fix PR?

xiaket reviewed Feb 22, 2026

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xiaket requested changes Feb 22, 2026

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Cyfarw9dd mentioned this pull request Feb 27, 2026

fix: separate ContextWindow from MaxTokens configuration #848

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nikolasdehor approved these changes Feb 28, 2026

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sipeed-bot bot added type: bug Something isn't working domain: agent domain: config labels Mar 3, 2026

is-Xiaoen mentioned this pull request Mar 12, 2026

[Agent refactor] Context management: boundaries, compression, and token budgeting #1439

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is-Xiaoen mentioned this pull request Mar 13, 2026

refactor(agent): context boundary detection, proactive budget check, and safe compression #1490

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yinwm closed this in 9c82b0b Mar 22, 2026

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fix(agent): decouple context_window from max_tokens#556

fix(agent): decouple context_window from max_tokens#556
repfigit wants to merge 2 commits intosipeed:mainfrom
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	ContextWindow int `json:"context_window,omitempty" env:"PICOCLAW_AGENTS_DEFAULTS_CONTEXT_WINDOW"`
	ContextWindow int `json:"context_window" env:"PICOCLAW_AGENTS_DEFAULTS_CONTEXT_WINDOW"`

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repfigit commented Feb 20, 2026

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