The page cache is one directory per document; the shipped suites measure under a UTF-8 locale (from dev 3321e7c9e36e)

sks/document/document_class.cpp

@@ -1,4 +1,6 @@
 #include "util.h"
+#include <functional>
+#include <sstream>
 #include "machine.h"
 #include "error.h"
 #include "kutil.h"
@@ -133,6 +135,30 @@ Document_class::Document_class(Machine& machine) : Klammer_base(machine)
 }
 
 
+// The cache directory of ONE document: the target's cache directory
+// (_latex_files, _html_pages) with a subdirectory per document, named by
+// the document's stem and a hash of its absolute path.  The cache used to
+// be one directory per target with an entry per chapter BASENAME, shared by
+// every document on the machine, and freshness is only "the source is
+// older than the entry": document A's kt/alpha.kt was served document B's
+// cached alpha whenever B had rendered later -- silently when the chapter
+// assembled, with B's error message when it did not (TODO 79, 2026-10-19).
+// The hash, not the path itself: a path can be long and hold any
+// character; the stem is for the eye.  A document given as a string
+// (ktext -s) has no file and is keyed by the working directory, where its
+// _text.kt is rewritten on every run.
+std::string Document_class::document_cache_directory(const std::string& target_cache) const
+{
+    const fs::path document = m_kt_root_filename.empty()
+        ? fs::current_path() / "_string_input"
+        : fs::absolute(fs::path(m_kt_root_filename)).lexically_normal();
+    std::ostringstream key;
+    key << document.stem().string() << "-" << std::hex
+        << std::hash<std::string>{}(document.generic_string());
+    return cache_directory(target_cache + "/" + key.str());
+}
+
+
 void Document_class::save_string_input_as_file()
 {
     if (!m_text.empty()) {

sks/document/document_class.h

@@ -193,7 +193,10 @@ public:
     std::vector<std::pair<std::string, std::string>> m_string_components {};
     std::vector<std::tuple<std::string,std::string,std::string,std::string>> m_toc_components {};
 
+    // The page cache of THIS document under a target's cache directory
+    // (document_class.cpp); set by each target's create_*_output_directories().
     std::string m_cache_dir {};
+    std::string document_cache_directory(const std::string& target_cache) const;
 };
 
 fs::path parse_input_filename(const std::string& s, const std::string& input_dir);

sks/document/document_html.cpp

@@ -190,7 +190,7 @@ std::string Document_class::create_html_output_directories()
         install_resolved_font(m_resolved_sans, output_directory);
         install_resolved_font(m_resolved_mono, output_directory);
     }
-    m_cache_dir = cache_directory("_html_pages");
+    m_cache_dir = document_cache_directory("_html_pages");
     if (m_no_cache && fs::exists(m_cache_dir)) {
         for (auto& entry : std::filesystem::directory_iterator(m_cache_dir)) {
             // What ":cache false" actually removed: a derived consequence of

sks/document/document_latex.cpp

@@ -12,7 +12,7 @@ std::string Document_class::create_tex_output_directories()
     (void)K::log(3);
     std::string output_directory =
         absolute_pathname(get("K_output_dir")); // + "/" + get("K_output_basename");
-    m_cache_dir = cache_directory("_latex_files");
+    m_cache_dir = document_cache_directory("_latex_files");
     if (!m_toc_only) { 
         if (!file_exists(output_directory, false, true)) {
             fs::create_directory(output_directory);