Add a Makefile target for plan viewer

Makefile

@@ -99,6 +99,18 @@ export-fixtures: ## Regenerate plan JSON for every tools/exporter/examples/*.sce
 examples: export-fixtures ## Regenerate fixtures from scenarios and run them through plan-runner against their oracles.
 	@cargo test -p plan-runner --test examples
 
+VIEWER_PORT ?= 8000
+
+.PHONY: viewer
+viewer: ## Serve the repository over HTTP for the plan viewer (override the port with VIEWER_PORT=...)
+	@if ! command -v python3 >/dev/null 2>&1; then \
+		echo "python3 not found. Enter the dev shell with 'make shell' (or 'nix develop') first."; \
+		exit 1; \
+	fi
+	@echo "Plan viewer: http://localhost:$(VIEWER_PORT)/tools/plan-viewer/index.html"
+	@echo "Example: http://localhost:$(VIEWER_PORT)/tools/plan-viewer/index.html?fixture=../../crates/plan-runner/fixtures/two_atom_join.json"
+	@python3 -m http.server $(VIEWER_PORT)
+
 .PHONY: shell
 shell: ## Enter the Nix dev shell defined in flake.nix
 	@nix develop

tools/plan-viewer/README.md

@@ -1,37 +1,18 @@
-# Plan Viewer
+## Query Plan Viewer
 
-A static HTML viewer for `plan-runner` fixtures.
-It renders the plan DAG, the input facts, and the relation computed at every plan node, so a fixture can be inspected without reading raw JSON.
+A static HTML viewer for `plan-runner` JSON files (the fixtures).
 
-## Usage
+### Usage
 
-Open [`index.html`](index.html) in a browser, then drop a fixture from `crates/plan-runner/fixtures/` onto the page or pick one with the file input.
+Open [`index.html`](index.html) in a browser, then drop a JSON file from [`crates/plan-runner/fixtures/`](../../crates/plan-runner/fixtures) onto the page.
 
-When the repository is served over HTTP, a fixture can also be loaded through a query parameter:
+Alternatively, you can run the commands below to serve the viewer locally:
 
 ```sh
-python3 -m http.server 8000
-# then open:
-# http://localhost:8000/tools/plan-viewer/index.html?fixture=../../crates/plan-runner/fixtures/two_atom_join.json
+make shell # Go into the Nix shells
+make viewer
 ```
 
-## What It Shows
+Then open the following URL in your browser (replace `two_atom_join.json` with the name of the plan you want to view)
 
-- **Plan DAG**: one box per plan node, laid out left to right by join depth, with `L` and `R` labels on join inputs and the root node marked.
-  Each box shows the node's output columns and row count.
-- **Selected Node**: a plain-language description of the operator, its output columns, and the full relation computed at that node.
-  Wildcard columns (names starting with an underscore) are dimmed.
-- **Result Bindings**: the root relation projected to the fixture's `expected_bindings` columns, with a per-row check against the oracle and a list of any expected rows the plan did not produce.
-- **Input Facts**: one table per relation in the fixture's schema.
-
-The header badge reports whether the evaluated bindings match the fixture's `expected_bindings` as a multiset, mirroring `plan_runner::verify`.
-
-## Scope
-
-The viewer re-implements the scan, semijoin, and natural join semantics of `crates/query-ops` and the execution order of `crates/plan-runner` in JavaScript, for display only.
-The Rust crates and their tests remain the correctness oracle; if the two ever disagree, the Rust behavior wins and the viewer has a bug.
-
-Unsupported cases:
-
-- plan node actions other than `scan` and `join`
-- fixtures without a `query` and `schema` block
+http://localhost:8000/tools/plan-viewer/index.html?fixture=../../crates/plan-runner/fixtures/two_atom_join.json