feat(models): surface and prevent silent max-tokens truncation

- Raise --max-tokens default from 4096 to 8192.
- Auto-raise MaxTokens toward the model's catalog Limit.Output (capped at
  32768) when the user hasn't set --max-tokens explicitly and no per-model
  modelSettings override applied. Prevents silent 4k/8k truncation on
  models that support 32k-262k output.
- Surface FinishReasonLength at turn end: the app now subscribes to
  TurnEndEvent and renders a system-message banner explaining the current
  cap, the model's known ceiling, and how to raise it. Previously the TUI
  swallowed 'length' stops, producing 'ghost' truncations.
- Export FinishReason* constants on pkg/kit (Stop, Length, ToolCalls,
  ContentFilter, Error, Other, Unknown) and fix stale comments that used
  Anthropic-style strings.
- Add Kit.MaxTokens() and Kit.MaxOutputLimit() SDK accessors, backed by
  Agent.GetMaxTokens() which correctly returns 0 for providers that
  suppress the param (e.g. Codex OAuth).
- Tests: rightSizeMaxTokens covers 7 paths (cap, raise, preserve,
  explicit flag, nil info, zero limit); handleTurnEnd covers length/
  non-length/nil-sendFn and the fallback message formatter.
- Docs: update configuration.md, cli/flags.md, and kit-extensions skill
  to reflect the new default and behavior.
This commit is contained in:
Ed Zynda
2026-04-16 23:12:10 +03:00
parent 633fa38b2b
commit 3bb20f5283
11 changed files with 429 additions and 10 deletions
+1 -1
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@@ -297,7 +297,7 @@ func init() {
flags.BoolVar(&noPromptTemplates, "no-prompt-templates", false, "disable prompt template discovery")
// Model generation parameters
flags.IntVar(&maxTokens, "max-tokens", 4096, "maximum number of tokens in the response")
flags.IntVar(&maxTokens, "max-tokens", 8192, "maximum number of output tokens per response (auto-raised up to 32768 for models with higher known output limits; see internal/models/embedded_models.json)")
flags.Float32Var(&temperature, "temperature", 0.7, "controls randomness in responses (0.0-1.0)")
flags.Float32Var(&topP, "top-p", 0.95, "controls diversity via nucleus sampling (0.0-1.0)")
flags.Int32Var(&topK, "top-k", 40, "controls diversity by limiting top K tokens to sample from")
+16
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@@ -1025,6 +1025,22 @@ func (a *Agent) GetModel() fantasy.LanguageModel {
return a.model
}
// GetMaxTokens returns the effective max output tokens the agent currently
// sends to the LLM provider, after per-model defaults, right-sizing, and any
// Anthropic thinking-budget adjustments. Returns 0 when no ModelConfig is
// attached (e.g. early init) or when the provider suppresses the parameter
// (e.g. Codex OAuth), which allows callers to differentiate "default" from
// "explicitly capped".
func (a *Agent) GetMaxTokens() int {
if a.skipMaxOutputTokens {
return 0
}
if a.modelConfig == nil {
return 0
}
return a.modelConfig.MaxTokens
}
// Close closes the agent and cleans up resources.
// If MCP tools are still loading in the background, Close waits for them
// to finish before closing connections to avoid resource leaks.
+60
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@@ -932,6 +932,8 @@ func (a *App) subscribeSDKEvents(sendFn func(tea.Msg), stepUsageSeen *atomic.Boo
Password: resp.Password,
Cancelled: resp.Cancelled,
}
case kit.TurnEndEvent:
a.handleTurnEnd(ev, sendFn)
}
}))
@@ -942,6 +944,64 @@ func (a *App) subscribeSDKEvents(sendFn func(tea.Msg), stepUsageSeen *atomic.Boo
}
}
// handleTurnEnd inspects a turn's final StopReason and surfaces actionable
// feedback to the user when the turn ended in a state they can act on.
//
// Today the only surfaced case is FinishReasonLength — the model hit its
// configured max_output_tokens budget and the reply was truncated. Without
// this banner the TUI used to swallow the truncation silently, leading to
// "ghost" cut-offs with no indication of why.
//
// Separated from subscribeSDKEvents so tests can exercise it directly via a
// stubbed sendFn without standing up a full Kit.
func (a *App) handleTurnEnd(ev kit.TurnEndEvent, sendFn func(tea.Msg)) {
if sendFn == nil {
return
}
if ev.StopReason != kit.FinishReasonLength {
return
}
sendFn(ExtensionPrintEvent{
Level: "info",
Text: a.formatMaxTokensTruncatedMessage(),
})
}
// formatMaxTokensTruncatedMessage builds the user-facing explanation for a
// truncated turn. It reports the active max_output_tokens budget and, when
// known, the model's catalog output ceiling so the user can judge how much
// headroom is available.
func (a *App) formatMaxTokensTruncatedMessage() string {
k := a.opts.Kit
if k == nil {
// Extremely early / test-stub case: still emit a useful generic hint.
return "⚠ Response truncated: the model hit the configured max_output_tokens limit. " +
"Raise it with --max-tokens N, KIT_MAX_TOKENS=N, or per-model " +
"modelSettings[provider/model].maxTokens in config."
}
current := k.MaxTokens()
ceiling := k.MaxOutputLimit()
model := k.GetModelString()
msg := "⚠ Response truncated: "
if model != "" {
msg += fmt.Sprintf("%s hit the configured max_output_tokens limit", model)
} else {
msg += "the model hit the configured max_output_tokens limit"
}
if current > 0 {
msg += fmt.Sprintf(" (%d)", current)
}
msg += "."
if ceiling > 0 && current > 0 && ceiling > current {
msg += fmt.Sprintf(" This model supports up to %d output tokens.", ceiling)
}
msg += "\n\nRaise it with --max-tokens N, KIT_MAX_TOKENS=N, " +
"or per-model modelSettings[provider/model].maxTokens in your config. " +
"Re-run the last prompt after raising it to get the full response."
return msg
}
// QuitFromExtension triggers a graceful shutdown. In interactive mode it
// sends a tea.QuitMsg to the program so the TUI exits cleanly. In
// non-interactive mode it cancels the root context, stopping any in-flight
+93
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@@ -3,10 +3,12 @@ package app
import (
"context"
"errors"
"strings"
"sync"
"testing"
"time"
tea "charm.land/bubbletea/v2"
kit "github.com/mark3labs/kit/pkg/kit"
)
@@ -666,3 +668,94 @@ func TestUpdateUsageFromTurnResult_contextTokensUsesAllCategories(t *testing.T)
expected, usage.contextCalls, usage.lastContextTokens)
}
}
// TestHandleTurnEnd_LengthEmitsWarning verifies that when the SDK reports a
// FinishReasonLength (max_output_tokens hit), the app surfaces a user-visible
// ExtensionPrintEvent with Level="info" so the TUI can render a banner
// instead of silently showing a truncated reply.
func TestHandleTurnEnd_LengthEmitsWarning(t *testing.T) {
app := New(Options{}, nil)
defer app.Close()
var mu sync.Mutex
var received []tea.Msg
sendFn := func(m tea.Msg) {
mu.Lock()
defer mu.Unlock()
received = append(received, m)
}
app.handleTurnEnd(kit.TurnEndEvent{StopReason: kit.FinishReasonLength}, sendFn)
mu.Lock()
defer mu.Unlock()
if len(received) != 1 {
t.Fatalf("expected 1 event on length stop, got %d", len(received))
}
ev, ok := received[0].(ExtensionPrintEvent)
if !ok {
t.Fatalf("expected ExtensionPrintEvent, got %T", received[0])
}
if ev.Level != "info" {
t.Errorf("expected Level=info, got %q", ev.Level)
}
if ev.Text == "" {
t.Error("expected non-empty warning text")
}
if !strings.Contains(ev.Text, "max_output_tokens") {
t.Errorf("warning text should mention max_output_tokens, got: %s", ev.Text)
}
}
// TestHandleTurnEnd_NonLengthIgnored verifies that ordinary stop reasons
// (stop, tool-calls, error, unknown, "") do not produce a warning banner.
func TestHandleTurnEnd_NonLengthIgnored(t *testing.T) {
app := New(Options{}, nil)
defer app.Close()
reasons := []string{
kit.FinishReasonStop,
kit.FinishReasonToolCalls,
kit.FinishReasonError,
kit.FinishReasonContentFilter,
kit.FinishReasonOther,
kit.FinishReasonUnknown,
"",
}
for _, r := range reasons {
var called bool
app.handleTurnEnd(kit.TurnEndEvent{StopReason: r}, func(m tea.Msg) {
called = true
})
if called {
t.Errorf("stop reason %q unexpectedly emitted a warning", r)
}
}
}
// TestHandleTurnEnd_NilSendFn guards against panics when no TUI listener is
// attached (e.g. early init or headless teardown).
func TestHandleTurnEnd_NilSendFn(t *testing.T) {
app := New(Options{}, nil)
defer app.Close()
// Should not panic with a nil sendFn.
app.handleTurnEnd(kit.TurnEndEvent{StopReason: kit.FinishReasonLength}, nil)
}
// TestFormatMaxTokensTruncatedMessage_NoKit verifies the fallback message
// when Options.Kit is nil (test/stub path).
func TestFormatMaxTokensTruncatedMessage_NoKit(t *testing.T) {
app := New(Options{}, nil)
defer app.Close()
msg := app.formatMaxTokensTruncatedMessage()
if msg == "" {
t.Fatal("expected non-empty fallback message")
}
for _, needle := range []string{"max_output_tokens", "--max-tokens", "KIT_MAX_TOKENS", "modelSettings"} {
if !strings.Contains(msg, needle) {
t.Errorf("fallback message missing %q:\n%s", needle, msg)
}
}
}
+36
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@@ -251,6 +251,11 @@ func CreateProvider(ctx context.Context, config *ProviderConfig) (*ProviderResul
// via CLI flag or global config.
ApplyModelSettings(config, modelInfo)
// Auto-raise MaxTokens toward the model's known output ceiling when the
// user hasn't explicitly set --max-tokens and no per-model override
// applied. Runs after ApplyModelSettings so explicit modelSettings win.
rightSizeMaxTokens(config, modelInfo)
// Create the base provider
var result *ProviderResult
var createErr error
@@ -489,6 +494,37 @@ func validateModelConfig(config *ProviderConfig, modelInfo *ModelInfo) {
}
}
// defaultRightSizeCap bounds auto-raised MaxTokens so that we don't silently
// allocate enormous output budgets for models with very high ceilings (e.g.
// Devstral at 262144, Mistral at 128000). Users who genuinely want more can
// pass --max-tokens explicitly or set modelSettings[...].maxTokens in config.
const defaultRightSizeCap = 32768
// rightSizeMaxTokens raises config.MaxTokens toward the model's known output
// ceiling when:
// - the user has not explicitly set --max-tokens (or the KIT_MAX_TOKENS env
// var, or the top-level max-tokens key in config.yaml), AND
// - no per-model override already bumped MaxTokens (ApplyModelSettings runs
// before this function), AND
// - modelInfo.Limit.Output is known and larger than the current MaxTokens.
//
// The raised value is capped at defaultRightSizeCap to keep accidental
// allocations reasonable on very-large-output models. This prevents the
// common "ghost" where the agent's reply is silently truncated at the 8192
// default even though the selected model supports 64k or 262k output tokens.
func rightSizeMaxTokens(config *ProviderConfig, modelInfo *ModelInfo) {
if modelInfo == nil || modelInfo.Limit.Output <= 0 {
return
}
if isExplicitlySet("max-tokens") {
return
}
target := min(modelInfo.Limit.Output, defaultRightSizeCap)
if config.MaxTokens < target {
config.MaxTokens = target
}
}
// clearConflictingAnthropicSamplingParams ensures that temperature and top_p are
// not both sent to the Anthropic API, which rejects requests containing both.
// When both are set (typically from defaults), top_p is cleared so that
+148
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@@ -0,0 +1,148 @@
package models
import (
"testing"
"github.com/spf13/pflag"
"github.com/spf13/viper"
)
// bindMaxTokensFlag wires a fresh pflag-backed "max-tokens" key into viper so
// isExplicitlySet behaves the same way it does in production. Returns a
// cleanup function that removes the binding so sibling tests see a clean
// state.
func bindMaxTokensFlag(t *testing.T, args []string) func() {
t.Helper()
fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
fs.Int("max-tokens", 8192, "")
if err := viper.BindPFlag("max-tokens", fs.Lookup("max-tokens")); err != nil {
t.Fatalf("BindPFlag: %v", err)
}
if err := fs.Parse(args); err != nil {
t.Fatalf("fs.Parse: %v", err)
}
return func() {
viper.Reset()
}
}
func TestRightSizeMaxTokens_RaisesWhenBelowCeiling(t *testing.T) {
cleanup := bindMaxTokensFlag(t, nil) // no args → flag.Changed = false
defer cleanup()
config := &ProviderConfig{MaxTokens: 8192}
modelInfo := &ModelInfo{
ID: "claude-sonnet-4-5",
Limit: Limit{Context: 200000, Output: 64000},
}
rightSizeMaxTokens(config, modelInfo)
if config.MaxTokens != 32768 {
t.Errorf("expected MaxTokens raised to defaultRightSizeCap (32768), got %d", config.MaxTokens)
}
}
func TestRightSizeMaxTokens_CapsAtDefaultRightSizeCap(t *testing.T) {
cleanup := bindMaxTokensFlag(t, nil)
defer cleanup()
config := &ProviderConfig{MaxTokens: 8192}
// Mistral Devstral has 262144 output — we should still cap at 32768.
modelInfo := &ModelInfo{
ID: "devstral-medium-latest",
Limit: Limit{Context: 262144, Output: 262144},
}
rightSizeMaxTokens(config, modelInfo)
if config.MaxTokens != defaultRightSizeCap {
t.Errorf("expected MaxTokens capped at %d, got %d", defaultRightSizeCap, config.MaxTokens)
}
}
func TestRightSizeMaxTokens_UsesExactOutputWhenBelowCap(t *testing.T) {
cleanup := bindMaxTokensFlag(t, nil)
defer cleanup()
config := &ProviderConfig{MaxTokens: 4096}
// Model with output limit smaller than the cap.
modelInfo := &ModelInfo{
ID: "gpt-4",
Limit: Limit{Context: 8192, Output: 8192},
}
rightSizeMaxTokens(config, modelInfo)
if config.MaxTokens != 8192 {
t.Errorf("expected MaxTokens raised to model output ceiling (8192), got %d", config.MaxTokens)
}
}
func TestRightSizeMaxTokens_DoesNotLowerCurrentValue(t *testing.T) {
cleanup := bindMaxTokensFlag(t, nil)
defer cleanup()
// User (via per-model settings, applied earlier) already bumped MaxTokens
// above the cap — we must not clobber their choice.
config := &ProviderConfig{MaxTokens: 100000}
modelInfo := &ModelInfo{
ID: "devstral-medium-latest",
Limit: Limit{Context: 262144, Output: 262144},
}
rightSizeMaxTokens(config, modelInfo)
if config.MaxTokens != 100000 {
t.Errorf("expected MaxTokens preserved at 100000, got %d", config.MaxTokens)
}
}
func TestRightSizeMaxTokens_RespectsExplicitFlag(t *testing.T) {
// Simulate `--max-tokens 4096` on the command line.
cleanup := bindMaxTokensFlag(t, []string{"--max-tokens", "4096"})
defer cleanup()
config := &ProviderConfig{MaxTokens: 4096}
modelInfo := &ModelInfo{
ID: "claude-sonnet-4-5",
Limit: Limit{Context: 200000, Output: 64000},
}
rightSizeMaxTokens(config, modelInfo)
if config.MaxTokens != 4096 {
t.Errorf("expected explicit --max-tokens to be preserved (4096), got %d", config.MaxTokens)
}
}
func TestRightSizeMaxTokens_NilModelInfo(t *testing.T) {
cleanup := bindMaxTokensFlag(t, nil)
defer cleanup()
config := &ProviderConfig{MaxTokens: 8192}
// Custom model / Ollama / unknown provider → no model info.
rightSizeMaxTokens(config, nil)
if config.MaxTokens != 8192 {
t.Errorf("expected MaxTokens unchanged with nil modelInfo, got %d", config.MaxTokens)
}
}
func TestRightSizeMaxTokens_ZeroOutputLimit(t *testing.T) {
cleanup := bindMaxTokensFlag(t, nil)
defer cleanup()
config := &ProviderConfig{MaxTokens: 8192}
// Model present in catalog but with no known output limit.
modelInfo := &ModelInfo{
ID: "unknown-model",
Limit: Limit{Context: 0, Output: 0},
}
rightSizeMaxTokens(config, modelInfo)
if config.MaxTokens != 8192 {
t.Errorf("expected MaxTokens unchanged with zero output limit, got %d", config.MaxTokens)
}
}
+39 -3
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@@ -110,6 +110,38 @@ func parseToolArgs(toolArgs string) map[string]any {
return nil
}
// ---------------------------------------------------------------------------
// Finish reason constants
// ---------------------------------------------------------------------------
// Finish reasons reported by the LLM provider on a completed turn. These
// mirror fantasy.FinishReason string values so comparisons against
// TurnEndEvent.StopReason / TurnResult.StopReason are stable across
// providers.
const (
// FinishReasonStop: the model produced a natural stop (e.g. stop sequence
// or end-of-turn signal).
FinishReasonStop = "stop"
// FinishReasonLength: the model hit the configured max_output_tokens
// budget. The response is truncated. Surface this to the user and
// consider raising --max-tokens / KIT_MAX_TOKENS / modelSettings[...]
// .maxTokens.
FinishReasonLength = "length"
// FinishReasonToolCalls: the model stopped to emit tool calls (normal
// mid-turn state during agentic loops).
FinishReasonToolCalls = "tool-calls"
// FinishReasonContentFilter: the provider's safety filter stopped
// generation.
FinishReasonContentFilter = "content-filter"
// FinishReasonError: the model stopped because of an error.
FinishReasonError = "error"
// FinishReasonOther: provider-specific reason that doesn't map to any of
// the above.
FinishReasonOther = "other"
// FinishReasonUnknown: the provider didn't report a finish reason.
FinishReasonUnknown = "unknown"
)
// ---------------------------------------------------------------------------
// Concrete event structs
// ---------------------------------------------------------------------------
@@ -124,9 +156,13 @@ func (e TurnStartEvent) EventType() EventType { return EventTurnStart }
// TurnEndEvent fires after the agent finishes processing.
type TurnEndEvent struct {
Response string
Error error
StopReason string // "end_turn", "max_tokens", "tool_use", "error", etc.
Response string
Error error
// StopReason is the LLM provider's finish reason for the final step of
// the turn. Compare against the FinishReason* constants — in particular,
// FinishReasonLength indicates the response was truncated because the
// agent hit its max_output_tokens budget.
StopReason string
}
// EventType implements Event.
+32 -2
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@@ -1451,8 +1451,9 @@ type TurnResult struct {
Response string
// StopReason indicates why the turn ended. Derived from the LLM
// provider's finish reason: "stop", "length" (max tokens), "tool-calls",
// "content-filter", "error", "other", "unknown".
// provider's finish reason: FinishReasonStop, FinishReasonLength (max
// output tokens reached), FinishReasonToolCalls, FinishReasonContentFilter,
// FinishReasonError, FinishReasonOther, FinishReasonUnknown.
StopReason string
// SessionID is the UUID of the session this turn belongs to.
@@ -2249,6 +2250,35 @@ func (m *Kit) GetTools() []Tool {
return m.agent.GetTools()
}
// MaxTokens returns the effective max output tokens currently configured for
// the agent. This is the value actually sent to the LLM provider on each
// request, after CLI/env/config resolution, per-model overrides, model-aware
// right-sizing, and any Anthropic thinking-budget adjustments.
//
// Returns 0 when the active provider suppresses the max_output_tokens
// parameter (e.g. OpenAI Codex OAuth) or when no model is configured yet.
// A non-zero value is the number that will cause a FinishReasonLength
// truncation if the model tries to generate beyond it.
func (m *Kit) MaxTokens() int {
if m.agent == nil {
return 0
}
return m.agent.GetMaxTokens()
}
// MaxOutputLimit returns the catalog-reported output ceiling for the current
// model in tokens, or 0 when the model isn't in the registry (custom models,
// new releases, Ollama, etc.). Pair with MaxTokens() to detect when the agent
// is configured well below what the model supports and surface a hint to the
// user.
func (m *Kit) MaxOutputLimit() int {
info := m.GetModelInfo()
if info == nil {
return 0
}
return info.Limit.Output
}
// extractFileParts returns all FilePart entries from a message's Content.
// Used to preserve image attachments when replacing user message text.
func extractFileParts(msg fantasy.Message) []fantasy.FilePart {
+1 -1
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@@ -93,7 +93,7 @@ api.OnAgentEnd(func(e ext.AgentEndEvent, ctx ext.Context) {
// e.Response string
// e.StopReason string — "error" (on failure), "completed" (when LLM returns
// empty stop reason), or the raw LLM provider value passed through
// (e.g. "stop", "end_turn", "max_tokens", "tool_use").
// (e.g. "stop", "length" (max output tokens hit), "tool-calls", "content-filter").
// To detect errors, check e.StopReason == "error".
// Do NOT compare against "completed" for success — instead check != "error".
})
+1 -1
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@@ -52,7 +52,7 @@ These flags control Kit's behavior. When a prompt is passed as a positional argu
| Flag | Short | Default | Description |
|------|-------|---------|-------------|
| `--max-tokens` | — | `4096` | Maximum tokens in response |
| `--max-tokens` | — | `8192` | Base cap for output tokens. Auto-raised per-model up to 32768 when the model's catalog ceiling is higher and no explicit value is set. |
| `--temperature` | — | `0.7` | Randomness 0.01.0 |
| `--top-p` | — | `0.95` | Nucleus sampling 0.01.0 |
| `--top-k` | — | `40` | Limit top K tokens |
+2 -2
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@@ -18,7 +18,7 @@ Create `~/.kit.yml`:
```yaml
model: anthropic/claude-sonnet-latest
max-tokens: 4096
max-tokens: 8192
temperature: 0.7
stream: true
```
@@ -28,7 +28,7 @@ stream: true
| Key | Type | Default | Description |
|-----|------|---------|-------------|
| `model` | string | `anthropic/claude-sonnet-latest` | Model to use (provider/model format) |
| `max-tokens` | int | `4096` | Maximum tokens in response |
| `max-tokens` | int | `8192` | Base cap for output tokens. Auto-raised per-model up to 32768 when the model's catalog ceiling is higher and no explicit value is set. Use [`modelSettings[provider/model].maxTokens`](#per-model-settings) to override per-model. |
| `temperature` | float | `0.7` | Randomness 0.01.0 |
| `top-p` | float | `0.95` | Nucleus sampling 0.01.0 |
| `top-k` | int | `40` | Limit top K tokens |