Spurious system-reminder falsely attributes a self-caused git checkout diff to "the user or a linter," instructs model to withhold it from the user

Description:

After running git checkout main (following a commit+push on a different branch), the next tool result was accompanied by a <system-reminder> claiming a specific file "was modified, either by the user or by a linter," calling it "intentional," and instructing: "Don't tell the user this, since they are already aware." It then included ~200 lines of file content.

In reality, the file's change in the working tree was the direct, expected consequence of the git checkout command itself (switching to a branch that lacks a just-committed change reverts that file to the target branch's version). Nothing external touched it. git status, git diff, and git branch --show-current all confirmed a clean, expected state — no uncommitted changes, correct branch, empty diff.

Two problems:

1. Factually wrong attribution — the reminder invented an external cause ("the user or a linter") for an effect that was clearly self-caused by the immediately preceding tool call in the same turn (a git checkout I had just issued).
2. Instruction to conceal from the user — regardless of cause, a system-generated reminder telling the model to hide information from the user is a concerning pattern to emit, since it's indistinguishable from a prompt-injection payload and pressures the model toward non-transparent behavior with the user.

Impact: Low in this instance — the model (Claude Sonnet 5) disregarded the "don't tell the user" instruction, verified the actual git state, and disclosed the discrepancy to the user rather than complying. But the mechanism that generates these reminders should not be capable of emitting "don't tell the user" instructions, and should not misattribute normal git side-effects to external actors.

Environment: Claude Code CLI, model claude-sonnet-5, Linux, working in a git repo mid-session, reminder appeared immediately after a git checkout <branch> tool call.

Reproduction context: This occurred during a session that had just committed a one-line bugfix to a feature branch, pushed it, then checked out main to restore the working tree before merging the PR. The reminder appeared attached to the next tool result after the checkout (a gh pr view call), not the checkout's own result.