Add standalone Dream Maker structural linter

.github/workflows/dmlint.yml

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+name: Dream Maker structural lint
+
+on:
+  pull_request:
+    paths:
+      - "code/**/*.dm"
+      - "tools/dmlint/**"
+      - ".github/workflows/dmlint.yml"
+  push:
+    branches:
+      - master
+    paths:
+      - "code/**/*.dm"
+      - "tools/dmlint/**"
+      - ".github/workflows/dmlint.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  dmlint:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+      - name: Run unit tests
+        working-directory: tools/dmlint
+        run: python -m unittest -v
+      - name: Lint Dream Maker source
+        run: python tools/dmlint/dmlint.py

tools/dmlint/README.md

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+# dmlint
+
+`dmlint` is a standalone, dependency-free structural linter for Dream Maker
+source. It is intended for fast local feedback and CI checks without launching
+or embedding DreamMaker.
+
+It recursively indexes `code/**/*.dm`, tracks exact source locations, ignores
+syntax-like characters inside comments and strings, and validates:
+
+- terminated string literals and block comments;
+- paired parentheses, brackets, and braces;
+- balanced `#if`/`#ifdef`/`#ifndef` and `#endif` directives;
+- placement of `#else` and `#elif`;
+- required `#define` and `#include` arguments;
+- trailing whitespace.
+
+This tool deliberately does not claim compiler equivalence. Dream Maker has
+context-sensitive language behavior that a small standalone checker cannot
+reproduce safely. Rules here are conservative and modular so valid project
+syntax is not rejected merely because the linter does not understand it.
+
+## Usage
+
+From the repository root:
+
+```sh
+python3 tools/dmlint/dmlint.py
+python3 tools/dmlint/dmlint.py --format json
+python3 tools/dmlint/dmlint.py --warnings-as-errors
+```
+
+The optional positional argument selects another repository root. Text output
+uses the stable form:
+
+```text
+code/example.dm:12:8: error DM003: unexpected closing delimiter ']'
+```
+
+The exit status is `1` when an error is found, `2` for invocation or repository
+layout errors, and `0` otherwise. `--warnings-as-errors` also returns `1` for
+warning-only output.
+
+## Tests
+
+```sh
+cd tools/dmlint
+python3 -m unittest -v
+```
+
+The tests cover comment/string handling, exact locations, delimiter and
+preprocessor validation, recursive discovery, machine-readable output, and
+exit-code behavior.
+
+## Architecture and extension
+
+`tokenize` performs one linear pass and emits only syntax-significant tokens,
+making repository-scale cost proportional to bytes read. Validation functions
+consume that token stream independently and return immutable `Diagnostic`
+objects. `line_diagnostics` demonstrates a source-line rule that does not need
+tokens.
+
+To add a rule:
+
+1. write a pure function accepting tokens or source lines plus the path;
+2. return diagnostics with a unique code, precise location, and actionable
+   message;
+3. call it from `lint_text`;
+4. add positive and negative tests, especially for comments and strings.
+
+The implementation uses only the Python standard library and never shells out
+to DreamMaker or another parser.