feat: add typst inline equation preview

Mirrors the existing LaTeX fragment integration but uses the `typst`
CLI to compile `$...$' math fragments into PNGs that are then displayed
inline through the existing kitty-graphics overlay pipeline.

- New section in kitty-graphics.el: customs (typst-command, ppi,
  text-size, preamble), SHA-1 cached PNGs under /tmp/kitty-gfx-typst,
  Emacs face-foreground -> typst rgb() hex conversion.
- Two autoloaded commands: `kitty-gfx-typst-preview' and
  `kitty-gfx-typst-clear-preview', region-aware.
- Regex skips backslash-escaped dollars (\\$not math\\$).
- justfile with recipes: compile/lint/load + per-feature test-* and
  headless typst-render / typst-show.
- tests/test-typst.typ fixture with inline, display, mixed and
  edge-case fragments.
- AGENTS.md updated: test instructions, dependency note, issue marked
  done.

Closes #7. Parent #5.

1 files changed, 103 insertions, 0 deletions

diff --git a/justfile b/justfile
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--- /dev/null
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+# kitty-graphics.el -- developer task runner
+#
+# Requires: just, emacs, typst (for typst tests), imagemagick (for sixel).
+# Run `just` to list recipes.
+
+set shell := ["bash", "-cu"]
+
+EMACS  := env_var_or_default("EMACS", "emacs")
+TERM_  := env_var_or_default("KGFX_TERM", "xterm-256color")
+SRC    := "kitty-graphics.el"
+
+# Default: list recipes
+default:
+    @just --list --unsorted
+
+# --- Build / lint -----------------------------------------------------------
+
+# Byte-compile (primary lint check)
+compile:
+    rm -f {{SRC}}c
+    {{EMACS}} -Q -batch -f batch-byte-compile {{SRC}}
+
+# Byte-compile, treat warnings as errors
+lint:
+    rm -f {{SRC}}c
+    {{EMACS}} -Q -batch --eval '(setq byte-compile-error-on-warn t)' \
+        -f batch-byte-compile {{SRC}}
+
+# Load-test: file evaluates without error
+load:
+    {{EMACS}} -Q -batch -l {{SRC}} -f kill-emacs
+
+# Remove generated artifacts
+clean:
+    rm -f {{SRC}}c
+    rm -rf /tmp/kitty-gfx-typst /tmp/kitty-gfx-sixel-*.six /tmp/kitty-gfx.log
+
+# --- Interactive tests (open terminal Emacs) --------------------------------
+
+# Test typst inline equations (M-x kitty-gfx-typst-preview after open)
+test-typst:
+    @echo ">> M-x kitty-gfx-typst-preview     to render"
+    @echo ">> M-x kitty-gfx-typst-clear-preview to clear"
+    TERM={{TERM_}} {{EMACS}} -nw -Q -l {{SRC}} \
+        --eval "(kitty-graphics-mode 1)" \
+        --eval "(setq kitty-gfx-debug t)" \
+        tests/test-typst.typ
+
+# Test org-mode inline images -- C-c C-x C-v after open
+test-org:
+    TERM={{TERM_}} {{EMACS}} -nw -Q -l {{SRC}} \
+        --eval "(kitty-graphics-mode 1)" \
+        tests/test-kitty-gfx.org
+
+# Test text sizing protocol (OSC 66) on org headings
+test-headings:
+    TERM={{TERM_}} {{EMACS}} -nw -Q -l {{SRC}} \
+        --eval "(setq kitty-gfx-heading-sizes-auto t)" \
+        --eval "(kitty-graphics-mode 1)" \
+        tests/test-kitty-gfx.org
+
+# Test image-mode rendering
+test-image:
+    TERM={{TERM_}} {{EMACS}} -nw -Q -l {{SRC}} \
+        --eval "(kitty-graphics-mode 1)" \
+        tests/test-image.png
+
+# Test doc-view / PDF rendering
+test-pdf:
+    TERM={{TERM_}} {{EMACS}} -nw -Q -l {{SRC}} \
+        --eval "(kitty-graphics-mode 1)" \
+        tests/test-document.pdf
+
+# Test markdown-overlays integration
+test-markdown:
+    TERM={{TERM_}} {{EMACS}} -nw -Q -l {{SRC}} \
+        --eval "(kitty-graphics-mode 1)" \
+        tests/test-markdown.md
+
+# Test LaTeX fragment preview in org-mode (C-c C-x C-l on a fragment)
+test-latex:
+    TERM={{TERM_}} {{EMACS}} -nw -Q -l {{SRC}} \
+        --eval "(kitty-graphics-mode 1)" \
+        tests/test-kitty-gfx.org
+
+# --- Headless typst checks --------------------------------------------------
+
+# Compile a typst fragment headlessly, print the PNG path
+typst-render fragment="$x^2 + y^2 = z^2$":
+    {{EMACS}} -Q -batch -L . -l {{SRC}} --eval '(progn \
+        (setq kitty-gfx-debug t) \
+        (let ((png (kitty-gfx--typst-render "{{fragment}}"))) \
+          (princ (format "png=%s exists=%s\n" png (and png (file-exists-p png))))))'
+
+# Render fragment and open PNG with xdg-open
+typst-show fragment="$integral_(-oo)^(+oo) e^(-x^2) dif x = sqrt(pi)$":
+    @png=$({{EMACS}} -Q -batch -L . -l {{SRC}} --eval '(princ (kitty-gfx--typst-render "{{fragment}}"))' 2>/dev/null); \
+        echo "png=$png"; \
+        [ -n "$png" ] && xdg-open "$png"
+
+# Tail the kitty-gfx debug log (set kitty-gfx-debug to t to populate)
+log:
+    tail -f /tmp/kitty-gfx.log