fix(pwntools): let callers widen the artifact input bound (#2486)

* fix(pwntools): let callers widen the artifact input bound

The pwntools adapters rejected every artifact over 32 MiB before any
analysis ran, and nothing in configuration, environment, CLI or MCP
could raise that bound, so real recorded core dumps stayed unanalyzable.

Resolve the bound from REA_PWNTOOLS_MAX_INPUT_BYTES in front of the
shipped default. An absent value keeps 32 MiB, and a value outside
1..1073741824 bytes is refused as unusable provider configuration before
the artifact is read instead of falling back silently.

* fix(pwntools): name the bound variable in its own refusal

An unusable REA_PWNTOOLS_MAX_INPUT_BYTES travelled through the shared
engine-absence helper, which always stamped configuration_key
REA_PWNTOOLS_PYTHON, so a caller following that field was pointed at the
Python executable instead of the bound it had just set. The guide also
described the refusal as an invalid request while the decoder reports
provider_unavailable.

Let the failure context carry the key under review and pass the bound's
own name at that call site, then state the code callers actually receive
in the guide. Assert the key on the projected rejection so the engine
default and the bound override each stay attributed to the right setting.

---------

Co-authored-by: morluto <76467478+morluto@users.noreply.github.com>

docs/binary-diagnostics.md

@@ -98,8 +98,10 @@ section, symbol, mitigation or linkage views. The default `complete` detail and
 CLI output are unchanged.
 
 Complete results have a 32 MiB input, 64 MiB reply, 1 MiB combined diagnostics
-and 30-second owned command deadline. The reply budget applies to the decoder
-record; the CLI/MCP Evidence envelope adds copies and encoding overhead. The
+and 30-second owned command deadline. `REA_PWNTOOLS_MAX_INPUT_BYTES` raises the
+input bound alone, up to 1 GiB; the reply and deadline bounds are unchanged. The
+reply budget applies to the decoder record; the CLI/MCP Evidence envelope adds
+copies and encoding overhead. The
 pinned MCP SDK defaults to a 10 MiB receive buffer. Large complete results need
 a caller-configured `StdioClientTransport({ maxBufferSize: ... })` and a matching
 server `REA_MCP_MAX_RESPONSE_BYTES`. See [MCP delivery budgets](mcp-contracts.md#tool-results).