feat(context): make the context-window fallback configurable (#480)

Motivated by #429. The context widgets already read the real window from Claude Code's context_window.context_window_size when present, and from a [1m]-style model-name hint otherwise; only the final fallback was a hard-coded 200k. On an older Claude Code that does not report the window size for a 1M-context model, that fallback made the bar read against 200k (e.g. 750k/200k, pinned full).

Demote the hard-coded 200k to the default of a configurable last-resort fallback, CCSTATUSLINE_CONTEXT_SIZE_FALLBACK (positive integer, ignored when unset or invalid), mirroring CCSTATUSLINE_WIDTH. The live status field and model-name hint still take precedence, so the override only applies when the window is otherwise unknown.

Author: CorticalCode

docs/USAGE.md

@@ -44,7 +44,7 @@ bun run example
 - **Tokens Input** / **Tokens Output** / **Tokens Cached** / **Tokens Total** - Show current-session token counts. Input/output prefer cumulative transcript metrics and fall back to `context_window.total_input_tokens` / `context_window.total_output_tokens` when transcript metrics are unavailable; cached/total use transcript metrics.
 - **Cache Hit Rate** / **Cache Read** / **Cache Write** - Show prompt-cache efficiency. Cache Hit Rate uses cache reads divided by cache reads plus cache writes; Cache Read and Cache Write include each value's share of prompt context. They default to the latest turn from `context_window.current_usage`, can switch to cumulative session totals, and can hide when empty.
 - **Input Speed** / **Output Speed** / **Total Speed** - Show session-average token throughput with an optional per-widget rolling window (`0-120` seconds; `0` = full-session average).
-- **Context Length** / **Context Window** / **Context %** / **Context % (usable)** / **Context Bar** - Show current context length, total context window size, used/remaining percentage, usable-window percentage, or a progress bar.
+- **Context Length** / **Context Window** / **Context %** / **Context % (usable)** / **Context Bar** - Show current context length, total context window size, used/remaining percentage, usable-window percentage, or a progress bar. The window size is taken from Claude Code's reported `context_window.context_window_size` when present, then from a model-name hint (e.g. a `[1m]` suffix), and finally from a fixed fallback. Set `CCSTATUSLINE_CONTEXT_SIZE_FALLBACK` to a positive integer to override that last-resort fallback (defaults to `200000`) — useful when an older Claude Code does not report the window size for a 1M-context model, so the bar would otherwise read against 200k.
 - **Compaction Counter** - Show how many context compactions have been detected in the current session by scanning transcript compaction markers. It can render as icon plus number, text plus number, or number-only, and can hide while the count is zero. Two optional, independent per-item add-ons toggle extra detail: a trigger split (`↻ 3 (2 auto, 1 manual)`; a compaction whose trigger is missing or unrecognized is bucketed as `unknown`) and tokens reclaimed (`↻ 3 ↓887.0k`, each compaction's `preTokens - postTokens` floored at 0 and summed, shown only when greater than 0 — so very old transcripts predating the `postTokens` field display nothing).
 - **Session Usage** / **Weekly Usage** / **Weekly Sonnet Usage** / **Weekly Opus Usage** / **Extra Usage Utilization** / **Extra Usage Remaining** / **Extra Usage Used** / **Block Timer** / **Block Reset Timer** / **Weekly Reset Timer** - Show usage percentages, monthly pay-as-you-go overage usage, and current block/reset timing. The all-models weekly bar covers `seven_day` from the usage API; the per-model variants surface the `seven_day_sonnet` and `seven_day_opus` buckets that Claude Code's own `/usage` panel shows. Extra usage widgets accept known extra-usage state as complete when an account has no monthly limit configured, avoid repeated refetches and stale `[Timeout]` output, and format amounts with the API-reported billing currency when available. Session and weekly usage bars can show a time cursor; reset timers can show remaining time, progress, or exact reset date/time with timezone and locale controls.
 

src/utils/__tests__/model-context.test.ts

@@ -1,4 +1,5 @@
 import {
+    afterEach,
     describe,
     expect,
     it
@@ -126,6 +127,58 @@ describe('getContextConfig', () => {
             expect(config.usableTokens).toBe(160000);
         });
     });
+
+    describe('CCSTATUSLINE_CONTEXT_SIZE_FALLBACK override', () => {
+        afterEach(() => {
+            delete process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK;
+        });
+
+        it('uses the env value as the fallback when no window size is otherwise known', () => {
+            process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK = '1000000';
+            const config = getContextConfig('claude-sonnet-4-5-20250929');
+
+            expect(config.maxTokens).toBe(1000000);
+            expect(config.usableTokens).toBe(800000);
+        });
+
+        it('uses the env value as the fallback when the model is unknown', () => {
+            process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK = '500000';
+            const config = getContextConfig(undefined);
+
+            expect(config.maxTokens).toBe(500000);
+            expect(config.usableTokens).toBe(400000);
+        });
+
+        it('falls back to 200k when the env value is non-numeric', () => {
+            process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK = 'not-a-number';
+            const config = getContextConfig('claude-3-5-sonnet-20241022');
+
+            expect(config.maxTokens).toBe(200000);
+            expect(config.usableTokens).toBe(160000);
+        });
+
+        it('falls back to 200k when the env value is zero or negative', () => {
+            process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK = '0';
+            expect(getContextConfig(undefined).maxTokens).toBe(200000);
+
+            process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK = '-5';
+            expect(getContextConfig(undefined).maxTokens).toBe(200000);
+        });
+
+        it('does not override the live context_window_size from the status JSON', () => {
+            process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK = '500000';
+            const config = getContextConfig('claude-3-5-sonnet-20241022', 1000000);
+
+            expect(config.maxTokens).toBe(1000000);
+        });
+
+        it('does not override a [1m] model-name hint', () => {
+            process.env.CCSTATUSLINE_CONTEXT_SIZE_FALLBACK = '500000';
+            const config = getContextConfig('claude-sonnet-4-5-20250929[1m]');
+
+            expect(config.maxTokens).toBe(1000000);
+        });
+    });
 });
 
 describe('getModelContextIdentifier', () => {

src/utils/model-context.ts

@@ -10,6 +10,22 @@ interface ModelIdentifier {
 
 const DEFAULT_CONTEXT_WINDOW_SIZE = 200000;
 const USABLE_CONTEXT_RATIO = 0.8;
+const CONTEXT_SIZE_FALLBACK_ENV_VAR = 'CCSTATUSLINE_CONTEXT_SIZE_FALLBACK';
+
+// User-configurable last-resort fallback window size. Mirrors CCSTATUSLINE_WIDTH:
+// a positive integer read from the environment, ignored when unset or invalid.
+// Defaults to 200k so behavior is unchanged unless the user opts in.
+function getFallbackContextWindowSize(): number {
+    const raw = process.env[CONTEXT_SIZE_FALLBACK_ENV_VAR];
+    if (raw) {
+        const parsed = Number.parseInt(raw, 10);
+        if (Number.isFinite(parsed) && parsed > 0) {
+            return parsed;
+        }
+    }
+
+    return DEFAULT_CONTEXT_WINDOW_SIZE;
+}
 
 function toValidWindowSize(value: number | null | undefined): number | null {
     if (typeof value !== 'number' || !Number.isFinite(value) || value <= 0) {
@@ -82,10 +98,13 @@ export function getContextConfig(modelIdentifier?: string, contextWindowSize?: n
         };
     }
 
-    // Default to 200k for older models
+    // Last-resort fallback when neither the live status window size nor a
+    // model-name hint is available. Defaults to 200k, overridable via
+    // CCSTATUSLINE_CONTEXT_SIZE_FALLBACK.
+    const fallbackWindowSize = getFallbackContextWindowSize();
     const defaultConfig = {
-        maxTokens: DEFAULT_CONTEXT_WINDOW_SIZE,
-        usableTokens: Math.floor(DEFAULT_CONTEXT_WINDOW_SIZE * USABLE_CONTEXT_RATIO)
+        maxTokens: fallbackWindowSize,
+        usableTokens: Math.floor(fallbackWindowSize * USABLE_CONTEXT_RATIO)
     };
 
     if (!modelIdentifier) {