Make the text DSL a first-class, runnable graph description

CHANGELOG.md

@@ -7,6 +7,49 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- **`DslFilterGraph<InputType, OutputType>`** (`DslFilterGraph.hpp`) — runs
+  graphs described in the text DSL, making it a first-class way to describe
+  runtime graphs. Executes named-edge graphs with fan-out (every reader gets a
+  copy), fan-in merges (holes for dropped paths), drop propagation and dead
+  ends, and exposes the graph as a `MessageFilter`, so it can be nested or
+  registered as a stage. Construction instantiates and type-checks the whole
+  graph and throws a `GraphError` listing every located problem.
+- **`GraphOutputs`** — the ordered, optionally keyed results of a graph with
+  several outputs (`get` / `take` / `has`).
+- **`MergeFilter<OutputType>` / `registerMergeFilter`** (`MergeFilter.hpp`) —
+  fan-in stages for `(a, b) -> Merge`, using the same combiner signature as
+  `JoinFilter`.
+- **`validateDslGraph<In, Out>(text)`** — every build-time diagnostic without
+  throwing; `dsl::formatDiagnostic(s)` formats them as `line:column: message`.
+- `dsl::StageNode::fanIn` records whether a stage's inputs came from a group.
+
+### Changed
+- README, EXAMPLE.md and `apps/textPipeline` now describe runtime graphs in the
+  DSL first; the JSON format is documented as a supported alternative.
+- `dsl::toMermaid` now uses generated node ids (instead of edge names such as
+  `end` or the internal `$out0`), labels outputs as `out` / `out.<key>`, gives
+  each dead end its own node, and lists stage arguments.
+- DSL stages written without arguments now receive an empty config object
+  instead of `null`, matching JSON stages without `"config"`.
+- `dsl::parseGraphProgram` now uses the lexy-based parser, which moved into
+  `GraphLang.hpp`. It reports located, descriptive diagnostics (the lexy parser
+  used to report every problem as a bare "syntax error" at column 1), gives
+  stages their real columns, and supports decimal numbers, string escapes and
+  `#` inside strings. `GraphLangLexy.hpp` / `parseGraphProgramLexy` remain as
+  an alias.
+- DSL syntax errors say what was expected and what was found; a syntax error
+  ends its statement instead of producing follow-on errors; an unterminated
+  string no longer swallows the following lines; malformed or out-of-range
+  numbers and empty fan-in groups `()` are reported; messages say "argument"
+  instead of "config"; diagnostics are sorted by location.
+
+### Deprecated
+- The hand-written DSL parser. It moved to `GraphLangHandwritten.hpp` as
+  `dsl::parseGraphProgramHandwritten`, marked `[[deprecated]]`, and will be
+  removed in a future release. It produces the same results as
+  `dsl::parseGraphProgram`; the tests check the two against each other.
+
 ## [0.2.0] - 2026-09-15
 
 ### Added