docs(tools): document the abort message and the background call card; pin both with tests

packages/bash/pwsh-local/README.md

@@ -50,6 +50,6 @@ No direct invalidation; the named consumer owns any request-prefix changes.
 - **The command string is PowerShell text** — the `-Command` domain has no shell-quoting layer, but a model-facing command is parsed by PowerShell itself, so PowerShell syntax errors are command failures, not launch failures.
 - **A background spawn-failure note is single-delivery** — the subprocess service buffers no output for a process that never ran, so the executor injects `spawn failed: …` into exactly one `readOutput()` delta; a reader that discards that delta cannot recover it.
 - **Windows termination reports no signal** — a force-killed process settles as exit 1 with `signal: null`, so signal-based status classification (POSIX `killed`) does not apply on Windows; `kill()`-initiated stops still stamp `killed` directly.
-- **The encoding preamble precedes the command** — PowerShell requires `param(...)` and `using namespace`/`using assembly` statements at the very top of a script, so a command whose first statement is one of those cannot run under the UTF-8 output preamble; prefix such scripts with a no-op statement (or `& { … }`) first.
+- **The encoding preamble precedes the command** — PowerShell requires `param(...)`, `#requires`, and `using namespace`/`using assembly` statements at the very top of a script, so a command whose first statement is one of those cannot run under the UTF-8 output preamble; prefix such scripts with a no-op statement (or `& { … }`) first.
 
 Scrub-heuristic and spill-retention caveats live with [`dsh-subprocess-local`](../../subprocess/subprocess-local/README.md), which owns those mechanics.