chore: import upstream snapshot with attribution

examples/sandbox/docs/repo/README.md

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+# Credit Note Example Repo
+
+This tiny repo exists to support `examples/sandbox/docs/coding_task.py`.
+
+The task is intentionally small so a sandbox coding agent can inspect the repo, apply a minimal patch, and prove the fix with one targeted shell test command.

examples/sandbox/docs/repo/credit_note.sh

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+#!/bin/sh
+
+customer="$1"
+amount="$2"
+
+printf 'Credit note for %s: -$%s debit.\n' "$customer" "$amount"

examples/sandbox/docs/repo/task.md

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+# Task
+
+`credit_note.sh` formats a credit note incorrectly:
+
+- It prints a debit label instead of a credit label.
+- It preserves the sign instead of always showing the credited amount as positive.
+
+Use the smallest correct fix, then run this exact verification command from the `repo/` directory:
+
+`sh tests/test_credit_note.sh`
+
+If you use `apply_patch`, the patch paths must still be relative to the sandbox workspace root. That means the file paths should be `repo/credit_note.sh` and `repo/tests/test_credit_note.sh`.
+
+Do not change the test expectations.

examples/sandbox/docs/repo/tests/test_credit_note.sh

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+#!/bin/sh
+set -eu
+
+actual_positive="$(sh credit_note.sh Northwind 12.50)"
+if [ "$actual_positive" != 'Credit note for Northwind: $12.50 credit.' ]; then
+    printf 'expected positive case to pass, got: %s\n' "$actual_positive" >&2
+    exit 1
+fi
+
+actual_negative="$(sh credit_note.sh Northwind -12.50)"
+if [ "$actual_negative" != 'Credit note for Northwind: $12.50 credit.' ]; then
+    printf 'expected negative case to pass, got: %s\n' "$actual_negative" >&2
+    exit 1
+fi
+
+printf '2 passed\n'