G1 step 2: Gemini parsers (host-tested), and the memory decision (Q86)

lib/gemini: URLs split per RFC 3986 appendix B and resolved per section
5.2 (all 32 reference examples of 5.4 pass, with gemini:// for http://),
the request form (no fragment, lower-case host, never an empty path),
query encoding for input prompts, Saved Page paths; the response header
(status, category, MIME type and parameters, 1024-byte meta limit);
gemtext's line types; and display text for the Latin-1 fonts. 12 tests.

Q86, decided after step 1: free heap stays above 40 KB in steady state
and 20 KB during a handshake; a fetch won't start below 55 KB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

lib/gemini/src/gemtext.cpp

@@ -0,0 +1,97 @@
+#include "gemtext.h"
+
+#include <cstdint>
+
+namespace roro::gemini {
+
+namespace {
+std::string trim(const std::string& s) {
+    size_t a = s.find_first_not_of(" \t"), b = s.find_last_not_of(" \t");
+    return a == std::string::npos ? "" : s.substr(a, b - a + 1);
+}
+}  // namespace
+
+std::vector<GemLine> parseGemtext(const std::string& document) {
+    std::vector<GemLine> lines;
+    bool pre = false;
+    size_t start = 0;
+    while (start < document.size()) {
+        size_t end = document.find('\n', start);
+        if (end == std::string::npos) end = document.size();
+        std::string line = document.substr(start, end - start);
+        if (!line.empty() && line.back() == '\r') line.pop_back();
+        start = end + 1;
+
+        GemLine g;
+        if (line.compare(0, 3, "```") == 0) {
+            g.type = LineType::PreToggle;
+            g.text = trim(line.substr(3));
+            pre = !pre;
+        } else if (pre) {
+            g.type = LineType::Preformatted;
+            g.text = line;
+        } else if (line.compare(0, 2, "=>") == 0) {
+            g.type = LineType::Link;
+            std::string rest = trim(line.substr(2));
+            size_t gap = rest.find_first_of(" \t");
+            g.url = rest.substr(0, gap);
+            g.text = gap == std::string::npos ? "" : trim(rest.substr(gap));
+            if (g.text.empty()) g.text = g.url;
+        } else if (line.compare(0, 3, "###") == 0) {
+            g.type = LineType::Heading3;
+            g.text = trim(line.substr(3));
+        } else if (line.compare(0, 2, "##") == 0) {
+            g.type = LineType::Heading2;
+            g.text = trim(line.substr(2));
+        } else if (line.compare(0, 1, "#") == 0) {
+            g.type = LineType::Heading1;
+            g.text = trim(line.substr(1));
+        } else if (line.compare(0, 2, "* ") == 0) {
+            g.type = LineType::ListItem;
+            g.text = trim(line.substr(2));
+        } else if (line.compare(0, 1, ">") == 0) {
+            g.type = LineType::Quote;
+            g.text = trim(line.substr(1));
+        } else {
+            g.text = line;
+        }
+        lines.push_back(std::move(g));
+    }
+    return lines;
+}
+
+std::string displayText(const std::string& s) {
+    std::string out;
+    size_t column = 0;
+    for (size_t i = 0; i < s.size();) {
+        unsigned char c = static_cast<unsigned char>(s[i]);
+        if (c == '\t') {
+            do out += ' ';
+            while (++column % 4);
+            i++;
+            continue;
+        }
+        if (c < 0x80) {
+            out += static_cast<char>(c);
+            i++;
+        } else {
+            int len = (c & 0xE0) == 0xC0 ? 2 : (c & 0xF0) == 0xE0 ? 3 : (c & 0xF8) == 0xF0 ? 4 : 0;
+            bool valid = len > 0 && i + len <= s.size();
+            for (int k = 1; valid && k < len; k++) valid = (static_cast<unsigned char>(s[i + k]) & 0xC0) == 0x80;
+            if (!valid) {
+                out += '?';
+                i++;
+            } else {
+                uint32_t cp = len == 2 ? (c & 0x1F) : len == 3 ? (c & 0x0F) : (c & 0x07);
+                for (int k = 1; k < len; k++) cp = (cp << 6) | (static_cast<unsigned char>(s[i + k]) & 0x3F);
+                if (cp <= 0xFF) out.append(s, i, len);  // Latin-1: the fonts have it
+                else out += '?';
+                i += len;
+            }
+        }
+        column++;
+    }
+    return out;
+}
+
+}  // namespace roro::gemini