`read_file` now detects PDFs by extension or `%PDF-` magic bytes and
shells out to `pdftotext -layout` (poppler) to return plain text
directly to the model. New optional `pages` arg accepts `N` or `N-M`
slices so big papers can be read in pieces without burning context.
When `pdftotext` isn't on `$PATH`, the tool returns a structured
`{type: "binary_unavailable", kind: "pdf", reason, hint}` payload with
install hints (`brew install poppler` / `apt install poppler-utils`)
instead of crashing or returning UTF-8 garbage from a binary file.
Tests cover extension detection (case-insensitive), magic-byte sniffing
on extension-less files, the negative case for plain text, the pages
arg parser (single, range, whitespace, invalid forms), and the
binary_unavailable branch when `pdftotext` is absent.
.docx / .epub / .html stripping deferred — same dispatch can take more
extractors later.
Closes#34.
Hunter Bown
ba40ae4aac