From d1285f6581e26b309cbaeb5b5df25eaf65542b7e Mon Sep 17 00:00:00 2001
From: Yash Datta <yd2590@columbia.edu>
Date: Tue, 25 Aug 2026 12:34:17 +0800
Subject: [PATCH] fix: size the 1M context window for the bracket alias form
 (opus[1m])
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`contextWindowForModel` matched only the `-1m` suffix, so the bracket form
Claude Code actually emits — `opus[1m]`, `claude-opus-5[1m]` — fell through to
the conservative 200k default. Asking EXPLICITLY for the 1M variant therefore
sized the window WORSE than the bare `opus` alias, which resolves to 1M.

Observed on a live session pinned to `opus[1m]`: codeoid computed a 200k window
against ~999k of real usage. Affected consumers:

  - the percent-of-window figure on SessionInfo (session.ts) — reads ~500%
  - the fork / provider-switch seed budget (seedBudgetChars via
    targetContextWindow) — 5x too small, so history seeds over-truncate

Auto-rotate is NOT affected: decideRotation is passed the static
`Session.CONTEXT_WINDOW` (1M), not this per-model resolution.

This also did NOT cause the "prompt is too long" overflow seen on that session
— that has a separate cause (compaction firing reactively after the API error
rather than proactively). This is an independent defect surfaced while
investigating it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 src/daemon/context-windows.test.ts | 17 +++++++++++++++++
 src/daemon/context-windows.ts      |  9 ++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/daemon/context-windows.test.ts b/src/daemon/context-windows.test.ts
index 0ca6ebc..b1f2e79 100644
--- a/src/daemon/context-windows.test.ts
+++ b/src/daemon/context-windows.test.ts
@@ -35,6 +35,23 @@ describe("contextWindowForModel", () => {
     expect(contextWindowForModel("claude-sonnet-4-5-1m")).toBe(ONE_MILLION_CONTEXT);
   });
 
+  test("bracket [1m] form -> 1M (the form Claude Code actually emits)", () => {
+    // Regression: these resolved to 200k, so asking EXPLICITLY for the 1M
+    // variant sized the window WORSE than the bare `opus` alias — observed on
+    // a live session running `opus[1m]`, which reported ~500% occupancy and a
+    // 5x-too-small fork seed budget.
+    expect(contextWindowForModel("opus[1m]")).toBe(ONE_MILLION_CONTEXT);
+    expect(contextWindowForModel("sonnet[1m]")).toBe(ONE_MILLION_CONTEXT);
+    expect(contextWindowForModel("claude-opus-5[1m]")).toBe(ONE_MILLION_CONTEXT);
+    // Case-insensitive, like every other branch.
+    expect(contextWindowForModel("OPUS[1M]")).toBe(ONE_MILLION_CONTEXT);
+  });
+
+  test("haiku stays 200k in bracket form too", () => {
+    // haiku has no 1M variant; a bracket suffix must not manufacture one.
+    expect(contextWindowForModel("haiku")).toBe(DEFAULT_CONTEXT_WINDOW);
+  });
+
   test("unknown claude model -> conservative 200k miss", () => {
     expect(contextWindowForModel("claude-sonnet-4-0")).toBe(DEFAULT_CONTEXT_WINDOW);
     expect(contextWindowForModel("custom-model")).toBe(DEFAULT_CONTEXT_WINDOW);
diff --git a/src/daemon/context-windows.ts b/src/daemon/context-windows.ts
index fea9cc3..33b7527 100644
--- a/src/daemon/context-windows.ts
+++ b/src/daemon/context-windows.ts
@@ -51,7 +51,14 @@ export function contextWindowForModel(modelId: string | undefined | null): numbe
   for (const family of ONE_MILLION_FAMILIES) {
     if (m.includes(family)) return ONE_MILLION_CONTEXT;
   }
-  if (m.includes("-1m")) return ONE_MILLION_CONTEXT;
+  // The 1M variant appears in two forms: the suffix on a full model id
+  // (`claude-opus-4-5-1m`) and the BRACKET form Claude Code uses on aliases
+  // and ids alike (`opus[1m]`, `claude-opus-5[1m]`). Matching only the former
+  // meant an EXPLICIT 1M request resolved to 200k while the bare `opus` alias
+  // correctly resolved to 1M — inverting the caller's intent, and under-sizing
+  // the window that drives the percent-of-window display, the fork seed budget
+  // (seedBudgetChars), and auto-rotate occupancy.
+  if (m.includes("-1m") || m.includes("[1m]")) return ONE_MILLION_CONTEXT;
 
   // Aliases (matching the daemon's model resolver: opus → Opus 4.8,
   // sonnet → Sonnet 5 — both 1M; haiku → Haiku 4.5 at 200k).