v0.8.6: general mode, clipboard text, PDF text extraction

Working mode: --mode coding|general (CST_MODE, settings.json, /mode,
WebUI run settings). general swaps the default framing for a general
assistant one -- workflow, safety notes, tool wording (run_shell, the
subagents) -- and /status shows it; minimal (the paper profile) stays
byte-frozen. The prompt state carries the mode so a switch leaves a
system note in history.

Clipboard: clipboard_read / clipboard_write tools (16 MiB cap read,
default 64 KiB window; writing is a WRITE permission with a preview) on
pbcopy / wl-copy / xclip / pbpaste / wl-paste / xclip and the Win32
clipboard. In the TUI, /attach paste falls back to clipboard text when
there is no image on it.

PDF: a dependency-free text extractor (src/pdf_text.c): inflate,
Flate/ASCIIHex/ASCII85, PNG/TIFF predictors, layout-independent object
scan, object streams, page tree walk with inherited resources, content
lexer (Tj/TJ/'/" and the Td/TD/T*/Tm spacing heuristics), per-font
ToUnicode CMaps and inline images skipped. Encrypted files and pages
with no text layer are refused with the reason.

Attachments: /attach (a path or files dropped on the terminal) now take
images, PDFs and text. A PDF is stored as its text layer with the mime
still saying application/pdf and its page count; anything else has to be
UTF-8 text. Documents travel inline as text parts, so CST_NO_IMAGES and
text-only models no longer drop them, while images keep their old path.

Tests: test_pdf_text (plain, bare and zlib-framed Flate, inline image,
CID + ToUnicode, object stream, error paths), documents in test_attach,
inlined documents in test_llm_body, mode in test_config.

src/tools/agent_tools.c

@@ -7,6 +7,7 @@
 #include <string.h>
 
 #include "cst_tools.h"
+#include "cst_clipboard.h"
 #include "cst_util.h"
 #include "tools_internal.h"
 
@@ -106,3 +107,70 @@ int cst_tool_ask_user(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
                            1);
   return tool_set_resultf(r, 0, "user answered: %s", ans);
 }
+
+/* The system clipboard: what the user copied elsewhere. Reading needs no
+ * permission (READ); writing replaces what the user has copied (WRITE, so
+ * the confirmation frontier applies). */
+int cst_tool_clipboard_read(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
+                            cst_tool_result_t *r) {
+  (void)ctx;
+  char err[192];
+  char *text = NULL;
+  size_t n = 0;
+  if (cst_clipboard_text(&text, &n, err, sizeof(err)) != 0)
+    return tool_set_result(r, err, 1);
+  long cap = tool_arg_long(c, "max_bytes", 65536);
+  if (cap > 0 && (size_t)cap < n)
+    n = (size_t)cap;
+  cst_buf_t b = {0};
+  cst_buf_printf(&b, "clipboard text (%zu bytes%s):\n", (size_t)n,
+                 (size_t)cap < (size_t)n ? ", truncated" : "");
+  cst_buf_append(&b, text, n);
+  if (b.len && b.buf[b.len - 1] != '\n')
+    cst_buf_puts(&b, "\n");
+  free(text);
+  return tool_take_buf(r, &b, 0);
+}
+
+int cst_tool_clipboard_write(const cst_tool_ctx_t *ctx,
+                             const ctl_tool_call_t *c, cst_tool_result_t *r) {
+  (void)ctx;
+  size_t n = 0;
+  const char *text = tool_arg_n(c, "text", &n);
+  if (!text)
+    return tool_set_result(r, "error: missing text", 1);
+  char err[192];
+  if (cst_clipboard_set_text(text, n, err, sizeof(err)) != 0)
+    return tool_set_result(r, err, 1);
+  return tool_set_resultf(r, 0, "copied %zu bytes to the clipboard", n);
+}
+
+/* Confirmation preview: what the clipboard would hold afterwards. Clipboard
+ * text has no diff, so this is the text itself, cut to a readable size. */
+#define CLIP_PREVIEW_MAX 2000
+int cst_preview_clipboard_write(const cst_tool_ctx_t *ctx,
+                                const ctl_tool_call_t *c, char **out) {
+  (void)ctx;
+  size_t n = 0;
+  const char *text = tool_arg_n(c, "text", &n);
+  if (!text) {
+    *out = strdup("error: missing text");
+    return -1;
+  }
+  int lines = 0;
+  for (size_t i = 0; i < n; i++)
+    lines += text[i] == '\n';
+  size_t cut = n;
+  if (cut > CLIP_PREVIEW_MAX)
+    cut = cst_utf8_floor(text, CLIP_PREVIEW_MAX);
+  cst_buf_t b = {0};
+  cst_buf_printf(&b, "clipboard: replace with %zu bytes, %d line%s\n", n,
+                 lines + (n && text[n - 1] != '\n'), lines == 0 ? "" : "s");
+  cst_buf_append(&b, text, cut);
+  if (b.len && b.buf[b.len - 1] != '\n')
+    cst_buf_puts(&b, "\n");
+  if (cut < n)
+    cst_buf_printf(&b, "… (%zu more bytes)\n", n - cut);
+  *out = cst_buf_steal(&b);
+  return 0;
+}

src/tools/fs_tools.c

@@ -267,6 +267,14 @@ int cst_tool_view_image(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
   cst_attachment_t *a = cst_attach_import_file(session, full, err, sizeof(err));
   if (!a)
     return tool_set_resultf(r, 1, "error: cannot show %.200s: %s", path, err);
+  if (!cst_attach_is_image(a)) {
+    cst_attach_free(a);
+    return tool_set_resultf(
+        r, 1,
+        "error: %.200s is not an image; a text file or PDF reaches the model "
+        "through /attach <path> (a PDF becomes its text layer)",
+        path);
+  }
   snprintf(a->origin, sizeof(a->origin), "view_image");
   const char *d = tool_arg(c, "detail");
   if (d && (strcmp(d, "low") == 0 || strcmp(d, "high") == 0))

src/tools/registry.c

@@ -66,8 +66,9 @@ static const cst_tool_def_t TOOLS[] = {
       {"detail", S, 0, "low or high (provider hint; default auto)"}},
      CST_TP_READ, 0, cst_tool_view_image, NULL, NO_DYN},
     {"run_shell",
-     "Run a non-interactive shell command in the workspace root for builds, "
-     "tests, git and other CLIs (stdin is empty; long runs are killed). "
+     "Run a non-interactive shell command in the workspace root: builds, "
+     "tests, git, scripts, computations, data processing, other CLIs "
+     "(stdin is empty; long runs are killed). "
      "Returns stdout+stderr with colors stripped and long output cut to head "
      "+ tail. Prefer read_file/grep/glob/list_dir over cat/grep/find.",
      "Run a shell command in the workspace root (non-interactive, stdin is "
@@ -158,6 +159,19 @@ static const cst_tool_def_t TOOLS[] = {
      {{"question", S, 1, "the question"},
       {"options", S, 0, "suggested answers, one per line"}},
      CST_TP_ASK, 0, cst_tool_ask_user, NULL, NO_DYN},
+    {"clipboard_read",
+     "Read the text on the system clipboard — what the user copied outside "
+     "the workspace. Returns UTF-8 text.",
+     NULL,
+     {{"max_bytes", I, 0, "cap on the returned text (default 65536)"}},
+     CST_TP_READ, 0, cst_tool_clipboard_read, NULL, NO_DYN},
+    {"clipboard_write",
+     "Replace the system clipboard with text, so the user can paste it into "
+     "another app. Overwrites what they had copied.",
+     NULL,
+     {{"text", S, 1, "text to put on the clipboard"}},
+     CST_TP_WRITE, 0, cst_tool_clipboard_write, cst_preview_clipboard_write,
+     NO_DYN},
 };
 #define NTOOLS ((int)(sizeof(TOOLS) / sizeof(TOOLS[0])))
 

src/tools/tools_internal.h

@@ -46,6 +46,13 @@ int cst_tool_todo_write(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
                         cst_tool_result_t *r);
 int cst_tool_ask_user(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
                       cst_tool_result_t *r);
+/* Clipboard text (system clipboard, not the workspace). */
+int cst_tool_clipboard_read(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
+                            cst_tool_result_t *r);
+int cst_tool_clipboard_write(const cst_tool_ctx_t *ctx,
+                             const ctl_tool_call_t *c, cst_tool_result_t *r);
+int cst_preview_clipboard_write(const cst_tool_ctx_t *ctx,
+                                const ctl_tool_call_t *c, char **out);
 int cst_tool_web_fetch(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
                        cst_tool_result_t *r);
 int cst_tool_view_image(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,