server: (tools) add x-tool-cwd header

[ngxson]

Overview

Add support for x-tool-cwd header to specify the current working dir of the call.

Note that it's not a tool param, but is a header. It's meant to be set and managed by the harness (llama-ui). This should match the behavior of pi and claude code.

CC @allozaur

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: tests and tools_io_basic changes are AI-coded, the rest is human-coded

[ServeurpersoCom]

The Windows CI failures look like strcasecmp in get_header, it's not available there, I'll test on Windows and confirm when I get a chance:

diff --git a/tools/server/server-tools.cpp b/tools/server/server-tools.cpp
index 0983e62cd..0836d9d65 100644
--- a/tools/server/server-tools.cpp
+++ b/tools/server/server-tools.cpp
@@ -1202,9 +1202,13 @@ static std::vector<std::unique_ptr<server_tool>> build_tools() {
     return tools;
 }

+// header names are ASCII, the lookup folds case without depending on a platform specific strcasecmp
 static std::string get_header(const std::map<std::string, std::string> & headers, const std::string & key, std::string default_value = "") {
+    auto fold = [](char c) { return c >= 'A' && c <= 'Z' ? char(c + 32) : c; };
     for (const auto & h : headers) {
-        if (strcasecmp(h.first.c_str(), key.c_str()) == 0) {
+        if (h.first.size() == key.size() &&
+            std::equal(h.first.begin(), h.first.end(), key.begin(),
+                       [&fold](char a, char b) { return fold(a) == fold(b); })) {
             return h.second;
         }
     }

[ServeurpersoCom]

LGTM: Replacing strcasecmp with the std::transform + std::tolower lowering makes the header lookup fully portable, and I confirmed it builds fine on my physical Windows 11 box.

Small nit, non blocking: server-models.cpp already has its own static to_lower_copy() doing the same thing, so this is a second file-local copy rather than an actual reuse ? Might be worth hoisting a single helper into server-common at some point.