State the shape rules of var and the Run window's args rows

decisions/prompt-language.md

@@ -259,9 +259,9 @@ The owner's reason: "Simpler implementation. Simpler mental model for authors. T
 
 ### `var` is a guarded table of JSON data
 
-`var` is an empty proxy table over a hidden data table, and each table that an author reads from it is a view of the same kind. The proxy checks each write at the assigning line: a function, a userdata, or a thread raises an error that says the value `must be JSON data`, and a key that JSON data has no place for, such as a boolean or an index past the end of a list, raises an error that names the key. A view measures and iterates like the table it stands for: `#` gives the length of the data, `pairs` and `next` visit its entries, and `var.items[#var.items + 1] = x` appends to a list.
+`var` is an empty proxy table over a hidden data table, and each table that an author reads from it is a view of the same kind. The proxy checks each write at the assigning line, by the rules of `json.encode`: a function, a userdata, or a thread raises an error that says the value `must be JSON data`, and a table that mixes list items and named keys raises an error that names it. A write that would leave its table neither a list nor an object raises too, such as a boolean key, a named field in a list, or an index past the end of a list. A view measures and iterates like the table it stands for: `#` gives the length of the data, `pairs` and `next` visit its entries, and `var.items[#var.items + 1] = x` appends to a list.
 
-The proxy is empty because Lua calls `__newindex` only for a key that a table lacks, so only an empty table sees every write. The Engine sets `__len` on each view, and its own `pairs` and `next` read through one, so that an author treats a `var` table as a plain table.
+The proxy is empty because Lua calls `__newindex` only for a key that a table lacks, so only an empty table sees every write. The guard refuses a write that `var` cannot hold as JSON data, where the write is made, because the read-back of `var` at the end of the block would otherwise fail on it or drop a part of it with no message. The Engine sets `__len` on each view, and its own `pairs` and `next` read through one, so that an author treats a `var` table as a plain table.
 
 ### `sys` is a sealed table of facts about the run and the section entry
 

decisions/tasks-and-fanout.md

@@ -42,7 +42,7 @@ They are methods of `Scheduler` because the owners depend on each other through
 
 ### `tasks.spawn` starts a chain over a section and returns a handle at once
 
-`tasks.spawn(target, opts)` queues a new chain that starts at the target section, and returns before that chain runs. `opts.args` gives the chain its own arguments, a table of named fields or a string, by the rule of the second argument of `call` ([The prompt language](prompt-language.md)), and a chain that gets none reads its spawner's `args`. The handle is a plain table, `{ task = id }`, and every `tasks` function that names a task takes the handle or the id string. The `tasks` table has thirteen functions: `spawn`, `join_any`, `join`, `ready`, `status`, `pending`, `note`, `cancel`, `concurrency`, `receive`, `send`, `reply`, and `fanout`.
+`tasks.spawn(target, opts)` queues a new chain that starts at the target section, and returns before that chain runs. `opts.args` gives the chain its own arguments, a table of named fields or a string, by the rule of the second argument of `call` ([The prompt language](prompt-language.md)), and a chain that gets none reads its spawner's `args`. `opts` takes the keys `args`, `item`, and `index`, and any other key raises an error that names it, so a misspelled option fails at the call. The handle is a plain table, `{ task = id }`, and every `tasks` function that names a task takes the handle or the id string. The `tasks` table has thirteen functions: `spawn`, `join_any`, `join`, `ready`, `status`, `pending`, `note`, `cancel`, `concurrency`, `receive`, `send`, `reply`, and `fanout`.
 
 ### The chain that spawns a task owns it
 

decisions/workshop-app.md

@@ -194,7 +194,7 @@ The names are the Agent Client Protocol's because the draft of that protocol has
 
 ### `POST /prompts/contract` parses prompt text and returns what its front matter declares
 
-The Run window posts a prompt's name and text. The route calls `Prompt::parse` and answers a `ContractResponse` with `name`, `description`, `runvil`, `max_tool_iterations`, `input`, `output`, `uses`, `args`, and `models`. A prompt that fails to parse answers 422 with a code such as `parse_frontmatter` or `parse_lua`.
+The Run window posts a prompt's name and text. The route calls `Prompt::parse` and answers a `ContractResponse` with `name`, `description`, `runvil`, `max_tool_iterations`, `output`, `uses`, `args`, and `models`. `args` is the prompt's declaration as JSON Schema, as `ArgsSchema::as_json` returns it ([The prompt language](prompt-language.md)). A prompt that fails to parse answers 422 with a code such as `parse_frontmatter` or `parse_lua`.
 
 The route is in the server crate because it only parses a prompt: its work is independent of the granted-folder check, and in `workshop-workspace` it would be that crate's only reason to depend on the Engine.
 

decisions/workshop-ui.md

@@ -176,7 +176,7 @@ CodeMirror is a ready-made editor, and the interface isolates it from the rest o
 
 ### The Run window shows what a prompt declares, and its Run button has an empty click handler
 
-Run > New Run Window runs `workbench.action.newRunWindow`, which opens a `run` panel in the main zone and loads the focused editor's file. The panel posts the prompt's text to the server route `POST /prompts/contract` and draws one row for each front-matter key except `uses`. The owner's rule: "let's keep the UI simple, one row for each thing."
+Run > New Run Window runs `workbench.action.newRunWindow`, which opens a `run` panel in the main zone and loads the focused editor's file. The panel posts the prompt's text to the server route `POST /prompts/contract` and draws one row for each front-matter key except `uses`. For `args` it draws one row for each argument the prompt declares at the top level: a switch for a boolean, a number field for an integer or a number, a text field for a string, and a box of JSON text for a list or an object. A string named `text` gets a multiline box, because `text` is the Engine's name for free text. The owner's rule: "let's keep the UI simple, one row for each thing."
 
 The Run button exists so that the window has its final shape. Its click handler is empty because running a prompt from this window is still to be built (section 8).