mach_examples/llms-full.md

# MACH

C23 web framework. App = `config mach()` returning `(config){...}` of resources, databases, modules, etc. Each request runs a pipeline of steps over a shared per-request context. Memory, threads, and I/O are managed by the framework. Tasks and events are durable.

---

## CRITICAL RULES — read these BEFORE writing any code

Almost every bug a small model writes in MACH comes from breaking one of these.
Skim once, refer back often.

### Rule 1 — NEVER use dot notation in `{{ }}`

The character `.` is **forbidden** between `{{` and `}}` anywhere in any
template, SQL string, URL, or interpolated string. The MACH interpreter
treats `{{a.b}}` as an unknown key and renders it as the **empty string**.

You access nested data **only** by entering nested sections with
`{{#name}}...{{/name}}`. The shape of the template must mirror the shape
of the context.

> **Self-check before emitting any tag**: is there a `.` between `{{` and `}}`?
> If yes, the template is wrong. Stop, rewrite with sections.

#### Pattern A — Single root scalar (from `.context`)

A scalar seeded into root context is read directly. There is nothing to
"dot through" in this case; this pattern just shows the baseline.

```c
.context = {{"site_name", "MACH App"}}
```

```html
✅ <h1>{{site_name}}</h1>
```

#### Pattern B — One-row flat access (single-row `find()` / `query()` result)

Even a single-row result is stored as a **table**. Fields are not at
root scope. Open the section, then read the field.

```c
find({.set_key = "todo", .db = "todos_db",
  .query = "select id, title from todos where id = {{id}};"})
```

Context after the step:
```
{ todo: [ { id: 5, title: "Learn MACH" } ] }
```

```html
✅ {{#todo}}<h1>{{title}}</h1><p>id={{id}}</p>{{/todo}}

❌ {{todo.title}}                         renders ""
❌ <h1>{{title}}</h1>                     renders "" (not inside #todo)
❌ {{#todo}}{{todo.title}}{{/todo}}       renders "" (dot still banned)
```

#### Pattern C — After `join()`: parent + nested children

The most common nested-context scenario in MACH. Concurrent `query()`
produces two **sibling** tables; `join()` then **moves** the children
inside each parent record. After the join, the children are no longer
accessible at root — the template MUST enter the parent section to
reach them.

```c
query(
  {.set_key = "project", .db = "projects_db",
   .query = "select id, name from projects where id = {{id}};"},
  {.set_key = "tasks",   .db = "projects_db",
   .query = "select id, project_id, title from tasks where project_id = {{id}};"}
),
join(
  .target_table_key      = "project",
  .target_field_key      = "id",
  .nested_table_key      = "tasks",
  .nested_field_key      = "project_id",
  .target_join_field_key = "tasks"
),
```

Context shape, before vs after the join:
```
after query(): { project: [{id, name}],
                 tasks:   [{id, project_id, title}, ...] }              // siblings

after join():  { project: [{id, name,
                            tasks: [{id, project_id, title}, ...]}] }   // tasks now INSIDE project
```

```html
✅
{{#project}}
  <h1>{{name}}</h1>
  <ul>
    {{#tasks}}<li>{{title}}</li>{{/tasks}}
  </ul>
{{/project}}

❌ {{project.name}}                                 renders ""  (dot)
❌ {{project.tasks.title}}                          renders ""  (dot)
❌ {{#project}}{{tasks.title}}{{/project}}          renders ""  (dot)
❌ {{#project.tasks}}<li>{{title}}</li>{{/project.tasks}}   dot in section name
❌ {{#tasks}}<li>{{title}}</li>{{/tasks}}           renders nothing — after join(),
                                                       tasks lives INSIDE project,
                                                       not at root. No dot, but
                                                       still wrong: must open
                                                       {{#project}} first.
```

The last counter-example is the subtle one: a join doesn't *copy* the
children, it **moves** them. Iterating `{{#tasks}}` at root after the
join silently produces nothing, even though there's no dot.

#### Pattern D — 3+ levels of nested sections

After multiple `join()` steps, or from nested JSON returned by `fetch()`,
context can be arbitrarily deep. Walk down level by level with one
section per level.

Context shape:
```
{ org: [ { name: "Acme",
           projects: [ { title: "Site",
                         tasks: [ { label: "Design" }, { label: "Build" } ] } ] } ] }
```

```html
✅
{{#org}}
  <h1>{{name}}</h1>
  {{#projects}}
    <h2>{{title}}</h2>
    <ul>
      {{#tasks}}
        <li>{{label}}</li>
      {{/tasks}}
    </ul>
  {{/projects}}
{{/org}}

❌ {{org.name}}                                       renders ""
❌ {{org.projects.title}}                             renders ""
❌ {{org.projects.tasks.label}}                       renders ""
❌ {{#org}}{{projects.title}}{{/org}}                 renders ""
❌ {{#org.projects}}{{title}}{{/org.projects}}        dot banned in section names too
❌ {{#org}}{{#projects}}{{tasks.label}}{{/projects}}{{/org}}   still has a dot
```

#### Pattern E — Iterating an array of nested sections

A `{{#name}}...{{/name}}` block automatically loops when `name` is an array.
Every iteration enters one record. Nested arrays loop the same way inside.

Context shape:
```
{ projects: [
    { title: "A", tasks: [{ label: "x" }, { label: "y" }] },
    { title: "B", tasks: [{ label: "z" }] }
] }
```

```html
✅
<ul>
  {{#projects}}
    <li>
      <strong>{{title}}</strong>
      <ul>
        {{#tasks}}<li>{{label}}</li>{{/tasks}}
      </ul>
    </li>
  {{/projects}}
</ul>

❌ {{#projects}}{{tasks.label}}{{/projects}}     dot banned
❌ {{projects.title}}                            dot banned
❌ {{#projects.tasks}}...{{/projects.tasks}}     dot banned
```

**Recap.** All five cases — flat single-row access, post-`join()`
parent/children, 3+ level nesting, iteration of nested arrays — use
the **same one rule**: open a section for every level, then read fields
by their bare name. There is never a reason to type a `.` inside
`{{ }}`. If you find yourself writing one, the data shape is fine; the
template is wrong. Add a section.

And remember the silent failure mode from Pattern C: after a `join()`,
the joined-in table is no longer at root. `{{#tasks}}` at root after
joining tasks into project renders nothing — open `{{#project}}` first.

> **Helpers like `{{url:name}}`, `{{input:title}}`, `{{error:title}}`,
> `{{precision:total:2}}` use `:` (colon), not `.` (dot)** — those are
> not dot notation and are fully supported.

---

### Rule 2 — ONE database per DOMAIN, not one database per table

A database holds many tables. Group every table that belongs to the same
business domain into one database. **Do not** create one database per
table — that is the most common mistake a small model makes here.

#### ✅ Correct: one database per domain, many tables inside

A `projects` domain owning `projects`, `tasks`, `comments`, `tags`:

```c
.databases = {{
  .engine     = sqlite_db,
  .name       = "projects_db",                // one db for the whole domain
  .connect    = "file:projects.db?mode=rwc",
  .migrations = {
    "CREATE TABLE projects ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "name TEXT NOT NULL"
    ");",
    "CREATE TABLE tasks ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "project_id INTEGER NOT NULL REFERENCES projects(id),"
      "title TEXT NOT NULL"
    ");",
    "CREATE TABLE comments ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "task_id INTEGER NOT NULL REFERENCES tasks(id),"
      "body TEXT NOT NULL"
    ");",
    "CREATE TABLE tags ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "label TEXT NOT NULL"
    ");"
  }
}}
```

#### ❌ Wrong: one database per table

```c
// DO NOT do this. Four databases for one domain is wrong.
.databases = {
  {.engine=sqlite_db, .name="projects_db", .connect="file:projects.db?mode=rwc",
   .migrations={"CREATE TABLE projects (...);"}},
  {.engine=sqlite_db, .name="tasks_db",    .connect="file:tasks.db?mode=rwc",
   .migrations={"CREATE TABLE tasks (...);"}},
  {.engine=sqlite_db, .name="comments_db", .connect="file:comments.db?mode=rwc",
   .migrations={"CREATE TABLE comments (...);"}},
  {.engine=sqlite_db, .name="tags_db",     .connect="file:tags.db?mode=rwc",
   .migrations={"CREATE TABLE tags (...);"}}
}
```

> **Parent-child relationships are ONE domain, ONE database.** A project
> and its tasks, a blog and its comments, an order and its line items,
> a user and its sessions, a todo and its comments — these are all
> parent-child relations within a single domain. They live as separate
> **migrations on the same database**, joined later via `join()` if
> needed. Splitting them across `projects_db` + `tasks_db` (or
> `blogs_db` + `comments_db`, etc.) is the **wrong** model — it's the
> exact mistake the ❌ example above shows.

**Where the boundary actually goes.** A new database appears when a new
**module** appears, because each module owns its domain. The `todos`
module has one `todos_db` (containing `todos`, `comments`, `daily_stats`,
etc.). The `activity` module has its own `activity_db`. The `billing`
module has `billing_db`. One database per domain, one domain per module.
A new database appears with a new module, **not** with a new table.

Migrations are an array on the same database; they run in order, so a
later table can reference an earlier one with `REFERENCES`.

---

### Rule 3 — Concurrent queries: ONE step, MANY items (across databases too)

`query()` and `fetch()` run their items **in parallel**. Two separate
`query()` steps run **serially**. Whenever you need more than one query
or fetch and they don't depend on each other's results, put them in
**one** step. This works **even when the items hit different databases**.

#### ✅ Concurrent — one `query()` call with multiple items

Same database:
```c
query(
  {.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"},
  {.set_key = "count", .db = "todos_db", .query = "select count(*) as n from todos;"}
)
```

**Across multiple databases — still one step, still concurrent:**
```c
query(
  {.set_key = "user",     .db = "users_db",    .query = "select * from users where id = {{id}};"},
  {.set_key = "orders",   .db = "commerce_db", .query = "select * from orders where user_id = {{id}};"},
  {.set_key = "activity", .db = "activity_db", .query = "select * from events where user_id = {{id}};"}
)
```

Same rule for `fetch()`:
```c
fetch(
  {"https://api.x.dev/a", .set_key = "a"},
  {"https://api.y.dev/b", .set_key = "b"}
)
```

#### ❌ Serial — multiple steps, each waiting for the previous

```c
// DO NOT do this when the queries are independent. Three round-trips, in series.
query({.set_key = "user",     .db = "users_db",    .query = "..."}),
query({.set_key = "orders",   .db = "commerce_db", .query = "..."}),
query({.set_key = "activity", .db = "activity_db", .query = "..."})
```

Use separate steps **only** when a later query depends on a value the
earlier query produced. Otherwise: one step, many items.

---

### Rule 4 — SQL `{{values}}` are bound as prepared-statement parameters

In `query()` and `find()`, `{{interpolation}}` is **bound as a parameter**,
never spliced into the SQL string. SQL injection is impossible at the
framework level. Do not pre-quote, do not pre-escape.

```c
✅ query({.db = "db", .query = "insert into todos(title) values({{title}});"})
❌ query({.db = "db", .query = "insert into todos(title) values('{{title}}');"})  // double-quoted
```

For transactions, use `BEGIN` / `COMMIT` / `ROLLBACK` directly in your queries.

---

### Rule 5 — Each `query()` / `find()` item: positional asset name **OR** `.query`, never both

```c
✅ query({"get_todos", .set_key = "todos", .db = "todos_db"})         // SQL loaded by name from .context
✅ query({.set_key = "todos", .db = "todos_db", .query = "select ..."})  // SQL inlined
❌ query({"get_todos", .set_key = "todos", .db = "todos_db", .query = "..."})  // both → boot rejection
```

---

### Rule 6 — `find()` raises `http_not_found` on zero rows, `query()` does not

Otherwise the two are identical. Use `find()` for "must exist" lookups
(detail pages, by-id reads). Use `query()` for lists, counts, writes,
and anything where zero rows is a normal outcome.

---

### Rule 7 — No `malloc` / `free`, no threads, no mutexes, no locks

Per-request arena handles all memory. Reactors and the shared thread pool
handle all concurrency. Application code never calls these.

For a buffer in a pipeline: `char *buf = allocate(256);` (reclaimed when
the request ends). To clean up a pointer returned by an external library:
`defer_free(out);` (cleanup runs when the arena releases).

---

### Rule 8 — Resource-based, not route-based

Resources are referenced by **name**, never by hard-coded path:

```c
{{url:todos}}              // → /todos
{{url:todo:5}}             // → /todos/5  (literal arg)
{{url:todo:id}}            // → /todos/{id from context}
redirect("todo:{{id}}")    // 302 to /todos/{id}
reroute("todos")           // re-enter pipeline server-side, same request
```

Changing `/todos` to `/items` later means changing one `.url` field.
Every link, redirect, and reroute follows.

---

## Guide

A todo app, built one concept at a time. Each step shows only the new
pieces; carry forward the previous code.

### 1. A Page

Two resources, each with a GET pipeline. `{{url:name}}` resolves at render time.

```c
#include <mach.h>

config mach(){
  return (config) {
    .resources = {
      {"home", "/",
        .get = { render(.template =
          "<html><body><h1>Welcome</h1>"
          "<a href='{{url:todos}}'>My Todos</a>"
          "</body></html>") }
      },
      {"todos", "/todos",
        .get = { render(.template = "<h1>My Todos</h1><p>Nothing yet.</p>") }
      }
    }
  };
}
```

### 2. Show Data

Add SQLite. `query()` stores rows under `todos`. The template opens the
section to iterate (Rule 1: section, never dot).

```c
#include <sqlite.h>

// inside todos resource:
.get = {
  query({.set_key = "todos", .db = "todos_db",
    .query = "select id, title from todos;"}),
  render(.template =
    "<h1>My Todos</h1>"
    "<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>")
}

// inside config:
.databases = {{
  .engine     = sqlite_db,
  .name       = "todos_db",
  .connect    = "file:todos.db?mode=rwc",
  .migrations = {
    "CREATE TABLE todos ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "title TEXT NOT NULL"
    ");"
  },
  .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
}},
.modules = {sqlite}
```

To fetch two things at once, put both items in **one** `query()` call (Rule 3):
```c
query(
  {.set_key="todos", .db="todos_db", .query="select id, title from todos;"},
  {.set_key="count", .db="todos_db", .query="select count(*) as n from todos;"}
)
```

### 3. Accept Input

`validate()` → `query()` → `redirect()` (POST-redirect-GET). On success
`title` is promoted from `input:title` to app scope and bound as a
prepared parameter (Rule 4) in the SQL.

```c
.post = {
  validate({"title",
    .validation = validate_not_empty,
    .message    = "title cannot be empty"}),
  query({.db = "todos_db",
    .query = "insert into todos(title) values({{title}});"}),
  redirect("todos")
}
```

Add the form to the GET template; `{{input:title}}` repopulates after errors:
```html
<form method='post' action='{{url:todos}}'>
  <input name='title' value='{{input:title}}'>
  <button>Add</button>
</form>
```

### 4. Handle Errors

A failed `validate()` raises `http_bad_request`. A resource-scoped error
handler re-enters the GET pipeline with `reroute()`. Both `input:` and
`error:` scopes survive the reroute.

```c
.errors = {
  {http_bad_request, { reroute("todos") }}
}
```

```html
<input name='title' value='{{input:title}}'>
{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}
```

### 5. Nested Data

Fetch parent + children **concurrently** in one `query()` (Rule 3),
`join()` to nest, then enter the parent section to render. Comments
belong to the same domain as todos, so `comments` is a new **migration**
on the existing `todos_db` (Rule 2), not a new database.

```c
{"todo", "/todos/:id",
  .get = {
    validate({"id", .validation = validate_integer,
      .message = "must be an integer"}),
    query(
      {.set_key = "todo",     .db = "todos_db",
       .query = "select id, title from todos where id = {{id}};"},
      {.set_key = "comments", .db = "todos_db",
       .query = "select id, todo_id, body from comments where todo_id = {{id}};"}
    ),
    join(
      .target_table_key      = "todo",
      .target_field_key      = "id",
      .nested_table_key      = "comments",
      .nested_field_key      = "todo_id",
      .target_join_field_key = "comments"
    ),
    render(.template =
      "{{#todo}}"
        "<h1>{{title}}</h1>"
        "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
      "{{/todo}}")
  }
}
```

After `join()`, `comments` lives **inside** each `todo` record. Reach it
from within `{{#todo}}`. Iterating `{{#comments}}` at root after a join
renders nothing.

### 6. Tasks

Tasks run async on task reactors. Trigger with `task("name")` or via
`.cron`. Same task can be both. Tasks are **durable**: the process can
crash mid-task and resume at the failed step on next boot.

```c
// in POST pipeline:
.post = {
  validate({...}),
  query({...}),
  task("record_daily_stats"),
  redirect("todos")
}

// at config level:
.tasks = {
  {"record_daily_stats", {
    query({.db = "todos_db",
      .query = "insert into daily_stats(todo_count) "
               "select count(*) from todos;"})
  }, .cron = "0 0 * * *"}
}
```

If the task needs caller context, list keys under `.accepts`:
```c
{"recount_for_user", {
  query({.db="todos_db", .query="update users set ... where id = {{user_id}};"})
}, .accepts = {"user_id"}}
```

### 7. Modules & Events

A module is a `.c` file with a function returning `config`. It owns its
own resources, **its own database** (one per domain — Rule 2),
migrations, tasks, and event subscribers. Modules communicate **only**
through pub/sub events, never direct calls. `main.c` includes them and
registers them under `.modules`.

```
.
├── todos/todos.c        // config todos() { ... }
├── activity/activity.c  // config activity() { ... }
└── main.c
```

**`main.c`**:
```c
#include <mach.h>
#include <sqlite.h>
#include "todos/todos.c"
#include "activity/activity.c"

config mach(){
  return (config){
    .resources = {{"home", "/", .get = { render(.template = "<h1>Welcome</h1>") }}},
    .modules = {todos, activity, sqlite}
  };
}
```

**Publisher** declares `.publishes` and calls `emit()`:
```c
config todos(){
  return (config){
    .name = "todos",
    .publishes = {{"todo_created", .with = {"title"}}},
    .resources = {
      {"todos", "/todos",
        .post = {
          validate({"title", .validation = validate_not_empty}),
          query({.db = "todos_db",
            .query = "insert into todos(title) values({{title}});"}),
          emit("todo_created"),
          redirect("todos")
        }
      }
    }
    // ... own database (todos_db) here
  };
}
```

**Subscriber** declares an `.events` entry. Published keys (`title`)
arrive in context. Subscriber owns its own database (`activity_db`).
```c
config activity(){
  return (config){
    .name = "activity",
    .events = {
      {"todo_created", {
        query({.db = "activity_db",
          .query = "insert into activities(kind, ref) "
                   "values('created', {{title}});"})
      }}
    }
    // ... own database (activity_db) here
  };
}
```

When `.publishes` exists anywhere, MACH creates a `mach_events` database
and tracks delivery. Undelivered events replay on next boot.

### 8. External Assets

Once templates and SQL grow, extract them into files. Embed with
`(asset){#embed "file"}` in `.context`, then reference by name from
`render()`, `query()`, and `find()`. `.migrations` accepts assets directly.

```
todos/
├── todos.c
├── todos_list.mustache.html
├── get_todos.sql
├── create_todo.sql
└── create_todos_table.sql
```

**`todos/get_todos.sql`**
```sql
select id, title from todos;
```

**`todos/todos.c`** (excerpt):
```c
.resources = {
  {"todos", "/todos",
    .get  = { query({"get_todos", .set_key = "todos", .db = "todos_db"}),
              render("todos_list") },
    .post = { validate({"title", .validation = validate_not_empty}),
              query({"create_todo", .db = "todos_db"}),
              redirect("todos") }
  }
},
.context = {
  {"todos_list", (asset){#embed "todos_list.mustache.html"}},
  {"get_todos",  (asset){#embed "get_todos.sql"}},
  {"create_todo",(asset){#embed "create_todo.sql"}}
},
.databases = {{
  .engine     = sqlite_db,
  .name       = "todos_db",
  .connect    = "file:todos.db?mode=rwc",
  .migrations = {(asset){#embed "create_todos_table.sql"}}
}}
```

SQL `{{interpolation}}` works the same as inline (still parameter-bound).

### 9. External Data

`fetch()` makes an HTTP request and stores the response in context.
JSON is parsed into tables/records (nested JSON → nested context tables);
plain text stores as a string.

```c
.get = {
  fetch("https://api.quotable.io/random", .set_key = "quote"),
  render("home")
}
```

The Quotable API returns `{"author":"...","content":"..."}`, parsed into
a single-row table under `quote`. Template opens the section (Rule 1):
```html
{{#quote}}<blockquote>{{content}}, {{author}}</blockquote>{{/quote}}
```

Multiple items in one `fetch()` run concurrently, same as `query()`.
`fetch()` supports POST/PUT/PATCH/DELETE, custom headers, JSON or text
bodies, and `{{interpolation}}` in URLs.

---

## Reference

### Notation

- `{}` — single value or struct: `.get = { ... }`
- `{{}}` — array of structs: `.databases = {{ ... }}`
- Multiple elements: `.databases = {{...}, {...}}`
- Multiple step items: `query({...}, {...})`

### Context

Per-request scoped key-value store. Three scopes:
- `input:xxx` — raw request parameters
- `error:xxx` — validation/error data
- (unprefixed) — app scope: query results, validated inputs, `.context` values

`validate()` promotes from `input:` to app scope. Docker secrets land in
context. `.context` seeds variables and assets at the root. Assets baked
at compile time via `(asset){#embed "file"}`.

```c
.context = {
  {"site_name", "MACH App"},
  {"layout",    (asset){#embed "static/layout.mustache.html"}},
  {"get_todos", (asset){#embed "todos/get_todos.sql"}}
}
```

### Databases

Migrations are forward-only, index-based, applied once each in array
order, tracked in `mach_meta`. Seeds are idempotent. Multi-tenant via
`{{interpolation}}` in `.connect`; connections pooled with LRU eviction.

**Reminder (Rule 2): one database per domain, many tables.** Related
tables go as separate migrations on the same database.

```c
.databases = {{
  .engine     = sqlite_db,
  .name       = "blog_db",
  .connect    = "file:{{user_id}}_blog.db?mode=rwc",   // multi-tenant
  .migrations = {
    "CREATE TABLE blogs ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "title TEXT NOT NULL,"
      "content TEXT NOT NULL"
    ");",
    "CREATE TABLE comments ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "blog_id INTEGER NOT NULL REFERENCES blogs(id),"
      "body TEXT NOT NULL"
    ");"
  },
  .seeds = {"INSERT OR IGNORE INTO blogs(id, title, content) VALUES(1, 'Hi', 'First');"}
}}
```

**Engines:** `sqlite_db`, `postgres_db`, `mysql_db`, `redis_db`, `duckdb_db`

### Resource Pipelines

Each `.resources` entry is a named URL endpoint. Identified by name in
`{{url:name}}`, `redirect()`, `reroute()` with colon-separated positional
args (`name:arg1:arg2`) that fill `:params` in URL-pattern order. Args
can be literals or context keys.

- `{{url:todos}}` → `/todos`
- `{{url:todo:5}}` → `/todos/5` (literal)
- `{{url:todo:id}}` → reads `id` from current scope
- `{{url:org_todo:acme:5}}` → fills multiple `:params`

Path specificity is automatic: `/todos/active` beats `/todos/:id`. Verb
selection: HTTP method, or `?http_method=...` parameter (lets HTML forms
reach PATCH/DELETE/SSE).

**Fields:**
- `.name` *(pos)* — identifier
- `.url` *(pos)* — pattern with `:params`
- `.steps` *(pos)* — shared steps run before every verb (middleware slot)
- `.mime` — default response content type
- `.get .post .put .patch .delete` — verb pipelines (arrays of steps)
- `.sse` — persistent SSE channel; first positional is channel name
- `.errors` — terminal handlers keyed by error code
- `.repairs` — resumable handlers keyed by error code

```c
{"todo", "/todos/:id", {
  validate({"id", .validation = "^\\d+$", .message = "must be a number"})
},
  .mime  = mime_html,
  .get   = { find({"get_todo", .set_key = "todo", .db = "todos_db"}),
             render("todo") },
  .patch = { validate({"title", .validation = validate_not_empty, .message = "required"}),
             query({.db = "todos_db",
               .query = "update todos set title = {{title}} where id = {{id}};"}),
             redirect("todo:{{id}}") },
  .delete = { query({.db = "todos_db",
                .query = "delete from todos where id = {{id}};"}),
              redirect("todos") },
  .sse    = {"todo/{{id}}", sse(.event = "ready") },
  .errors = {{http_not_found, { render("404") }}}
}
```

**MIME types:** `mime_html`, `mime_txt`, `mime_sse`, `mime_json`, `mime_js`

### Template Helpers

`{{helper:args}}` — positional, **colon-separated** (not dot-separated).
Each arg is a literal or a context key.

| Helper | Purpose | Example |
|---|---|---|
| `{{raw:field}}` | emit without HTML-escape (default escapes) | `<div>{{raw:body_html}}</div>` |
| `{{precision:field:N}}` | numeric format with N decimals | `${{precision:total:2}}` |
| `{{input:field}}` | raw request param (form repopulation) | `<input value='{{input:title}}'>` |
| `{{error:field}}` | truthy when field has an error (use as section) | `{{#error:title}}!{{/error:title}}` |
| `{{error_message:field}}` | the validation/error message | `<span>{{error_message:title}}</span>` |
| `{{error_code:field}}` | HTTP status code for the field error | `{{error_code:title}}` |
| `{{url:name[:args]}}` | resource URL by name with positional args | `<a href='{{url:todo:id}}'>...</a>` |
| `{{asset:filename}}` | cache-busted URL for `public/` file | `<link href='{{asset:styles.css}}'>` |
| `{{csrf:token}}` | CSRF token (for query strings); sets cookie | `?csrf={{csrf:token}}` |
| `{{csrf:input}}` | hidden `<input>` carrying CSRF token | `<form>{{csrf:input}}...</form>` |

CSRF verification is automatic: MACH compares the incoming token to the
cookie (httponly/secure/samesite) and returns 403 on mismatch. Just emit
`{{csrf:token}}` or `{{csrf:input}}`.

### Pipeline Steps

Every step accepts `.if_context` and `.unless_context`.

#### validate

Regex-checks request parameters. On success, promotes `input:name` to
app scope. On failure, sets `error:name` and raises `http_bad_request`.
All validations in one call complete before the error fires (so all
errors arrive together for form re-rendering). Define your own:
`#define validate_zipcode "^\\d{5}$"`.

- `.param_key` *(pos)* — name of param
- `.validation` — regex string or built-in macro
- `.message` — human-readable error
- `.optional` — skip when param absent
- `.fallback` — default when param absent

```c
validate(
  {"email",  .validation = validate_email,     .message = "must be a valid email"},
  {"title",  .validation = validate_not_empty, .message = "cannot be empty"},
  {"page",   .fallback   = "1",
             .validation = "^\\d+$",            .message = "must be a number"},
  {"filter", .optional   = true,
             .validation = "^(active|done)$",   .message = "must be active or done"}
)
```

**Built-in validators:**
- Strings: `validate_not_empty`, `validate_alpha`, `validate_alphanumeric`, `validate_slug`, `validate_no_html`
- Numbers: `validate_integer`, `validate_positive`, `validate_float`, `validate_percentage`
- Identity: `validate_email`, `validate_uuid`, `validate_username`
- Dates: `validate_date`, `validate_time`, `validate_datetime`
- Web: `validate_url`, `validate_ipv4`, `validate_hex_color`
- Codes: `validate_zipcode_us`, `validate_phone_e164`, `validate_cron`
- Security: `validate_no_sqli`, `validate_token`, `validate_base64`
- Boolean: `validate_boolean`, `validate_yes_no`, `validate_on_off`

#### find & query

Both run database queries. **`find()` raises `http_not_found` on zero
rows; `query()` does not.** Otherwise identical.

`.set_key` stores the result as a **table** in context (always — even
single-row results, see Rule 1 Pattern B). Templates open the table as
a section to access fields. SQL is either inlined with `.query` OR
loaded by name from `.context` as the positional (Rule 5). Multiple
items in one step run **concurrently** (Rule 3), even across different
databases. Interpolated `{{values}}` are bound as prepared parameters
(Rule 4). For transactions: `BEGIN`/`COMMIT`/`ROLLBACK` in the SQL.

- `.template_key` *(pos)* — SQL asset name in `.context` (vs `.query`)
- `.query` — inline SQL string with `{{interpolation}}` (vs positional)
- `.set_key` — context key for result table
- `.db` — database name from `.databases`
- `.if_context` / `.unless_context` *(per item)* — conditionally include
  while other items run concurrently

```c
query(
  {"get_todos", .set_key = "todos", .db = "todos_db"},
  {.set_key = "count", .db = "todos_db",
   .query = "select count(*) as n from todos where user_id = {{user_id}};"},
  {.if_context = "show_urgent", .set_key = "urgent", .db = "todos_db",
   .query = "select id, title from todos where priority = 'high';"}
)
```

#### join

Nests records from one context table into each matching record of
another, in memory. After `join()`, the inner records live **inside**
each outer record. Templates must enter the outer section to reach the
nested data. `{{#comments}}` at root after a join is empty.

- `.target_table_key` — outer table receiving children
- `.target_field_key` — outer field to match
- `.nested_table_key` — inner table to nest
- `.nested_field_key` — inner field that points to outer
- `.target_join_field_key` — new field on outer holding matched inner records

Pattern: concurrent `query()` → `join()` → `render()`:
```c
query(
  {.set_key="blog",     .db="blog_db", .query="select id, title from blogs where id = {{id}};"},
  {.set_key="comments", .db="blog_db", .query="select id, blog_id, body from comments where blog_id = {{id}};"}
),
join(
  .target_table_key="blog", .target_field_key="id",
  .nested_table_key="comments", .nested_field_key="blog_id",
  .target_join_field_key="comments"
),
render(.template =
  "{{#blog}}"
    "<h1>{{title}}</h1>"
    "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
  "{{/blog}}")
```

Context shape:
```
after query(): { blog: [{id,title}],          comments: [{id,blog_id,body}, ...] }
after join():  { blog: [{id,title, comments: [{id,blog_id,body}, ...]}] }
```

#### fetch

HTTP request → context. JSON parsed into tables/records; text stored as
string. Multiple items in one step run concurrently.

- `.url` *(pos)* — URL with `{{interpolation}}`
- `.set_key` — context key for response
- `.method` — defaults `http_get`
- `.headers` — array of `{name, value}` pairs
- `.json` — context key serialized as JSON request body
- `.text` — context key sent as plain-text body

```c
fetch("https://api.payments.dev/charge",
  .set_key = "receipt",
  .method  = http_post,
  .headers = {
    {"Authorization",   "Bearer {{api_key}}"},
    {"Idempotency-Key", "{{order_id}}"}
  },
  .json = "order"
)
```

**HTTP methods:** `http_get`, `http_post`, `http_put`, `http_patch`, `http_delete`, `http_sse_method`

#### exec

Calls a C function or block with imperative access to context. Dispatched
to the shared thread pool (releases the reactor); pipeline resumes on
the original reactor when done. Use for blocking I/O or CPU work.
Trigger an error pipeline from inside via `error_set()`.

- *Block* *(pos)* — inline block
- `.call` — named C function

```c
exec(^(){
  auto t = get("challengers");
  record_set(table_get(t, 0), "opponent_id",
             record_get(table_get(t, 1), "id"));
})

exec(.call = assign_opponents)
```

**Imperative API** (in exec blocks/functions):
- Context: `get(name)`, `set(name, value)`, `has(name)`, `format(fmt)`
- Memory: `allocate(bytes)`, `defer_free(ptr)`
- Errors: `error_set(name, err)`, `error_get(name)`, `error_has(name)`
- Tables: `table_new()`, `table_count(t)`, `table_get(t, i)`, `table_add(t, r)`, `table_remove(t, r)`, `table_remove_at(t, i)`
- Records: `record_new()`, `record_set(r, name, value)`, `record_get(r, name)`, `record_remove(r, name)`

#### emit

Triggers a pub/sub event. Subscribers in other modules react via their
`.events` pipelines.
```c
emit("todo_created")
```

#### task

Enqueues a named job in the task database; calling pipeline continues
immediately.
```c
task("recount_todos")
```

#### sse

Pushes a Server-Sent Event. With `.channel`, broadcasts. Without, sent
only to the requesting client.

- `.channel` *(pos)* — broadcast channel with `{{interpolation}}`
- `.event` — SSE `event:` line
- `.data` — array of strings (one per `data:` line)
- `.comment` — `:` comment line (keep-alives)

```c
sse(
  .channel = "todos/{{user_id}}",
  .event   = "todo_updated",
  .data    = {"id: {{todo_id}}", "title: {{title}}"},
  .comment = "broadcast at {{timestamp}}"
)
```

#### ds_sse

Datastar-formatted SSE; provided by `datastar` module. Pushes DOM updates
and reactive state. Without channel goes to requesting client; with
channel broadcasts.

- `.channel` *(pos)* — broadcast channel
- `.target` — DOM element id
- `.mode` — fragment insertion mode
- `.elements` — render_config (positional is asset name; supports `.template`, `.engine`)
- `.signals` — JSON updating Datastar reactive state
- `.js` — JS snippet evaluated on client

```c
ds_sse("todos/{{user_id}}",
  .target   = "todo-list",
  .mode     = mode_prepend,
  .elements = {"todo_row"},
  .signals  = "{\"count\": {{count}}}",
  .js       = "window.scrollTo(0, 0)"
)
```

**Modes:** `mode_outer`, `mode_inner`, `mode_replace`, `mode_prepend`, `mode_append`, `mode_before`, `mode_after`, `mode_remove`

#### render

Outputs a Mustache template. Auto-escapes by default (`{{raw:field}}`
opts out). All field access follows Rule 1 — sections only, never dot.

- `.template_key` *(pos)* — asset name in `.context`
- `.template` — inline Mustache string
- `.status` — HTTP status (default `http_ok`)
- `.mime` — override content type
- `.engine` — `mustache` (default) or `mdm` (Markdown-with-Mustache)
- `.json_table_key` — context table to serialize as JSON response
  (sets `application/json`; nested tables → nested JSON)

```c
render("todos")
render(.template = "<h1>{{site_name}}</h1>")
render("not_found", .status = http_not_found)
render(.engine = mdm, .template = "# Welcome, {{user_name}}")
render(.json_table_key = "todos")
```

**HTTP statuses:** `http_ok` (200), `http_created` (201), `http_redirect` (302), `http_bad_request` (400), `http_not_authorized` (401), `http_not_found` (404), `http_error` (500)

#### headers & cookies

Set response headers/cookies. Values support `{{interpolation}}`.

```c
headers({{"X-Request-Id", "{{request_id}}"}, {"Cache-Control", "no-store"}})
cookies({{"session", "{{session_id}}"}})
```

#### redirect & reroute

`redirect()` sends a 302 to the client (browser navigates). `reroute()`
is server-side: re-enter the router and run another resource's pipeline
within the same request. Both take a resource identifier
`name[:arg1:arg2...]`. Args can be literals or context keys.

```c
redirect("todos")              // 302 /todos
redirect("todo:5")             // 302 /todos/5
redirect("todo:{{id}}")        // 302 /todos/{id from context}
redirect("org_todo:acme:5")    // 302 /orgs/acme/todos/5
reroute("todo:{{id}}")         // run pipeline in-process
```

#### nest

Group steps under a single shared `.if_context` / `.unless_context`.

```c
nest({query({...}), emit("urgent_todo"), render("urgent")},
  .if_context = "is_urgent")
```

### Conditionals

Every step accepts `.if_context` (run when key present) and
`.unless_context` (run when absent). Works on validated inputs, query
results, framework flags (`is_htmx`), or flags set from `exec()`.

```c
render("fragment",  .if_context = "is_htmx")
render("full_page", .unless_context = "is_htmx")

// multi-state: set flag in exec, then key off it:
exec(.call = classify_todo),
render("urgent_confirmation",   .if_context     = "is_urgent"),
render("standard_confirmation", .unless_context = "is_urgent")
```

### Error and Repair Pipelines

On failure, MACH searches handlers bottom-up: resource → module → root.
- **Errors** are terminal: send a response, end the request.
- **Repairs** are resumable: fix context, then resume the original
  pipeline at the step after the failure.

If no matching repair, falls through to errors. The `error` scope is
shared across `validate()` and `error_set()`: `{{error:name}}`,
`{{error_code:name}}`, `{{error_message:name}}`. Raw input remains in
`input:name`.

```c
.errors = {
  {http_not_found,    { render("404") }},
  {http_bad_request,  { render("form") }},
  {http_error,        { render("500") }}
},
.repairs = {
  {http_not_authorized, { exec(.call = refresh_session_token) }}
}
```

**Built-in error codes:** `http_ok` (200), `http_created` (201),
`http_redirect` (302), `http_bad_request` (400), `http_not_authorized`
(401), `http_not_found` (404), `http_error` (500). Any int works;
`#define err_quota_exceeded 723` for domain-specific.

### Event Pipelines

Internal pub/sub for cross-module communication. Publisher doesn't know
subscribers; subscribers don't know publishers. Adding a subscriber =
new module with `.events`; publisher unchanged.

When `.publishes` exists anywhere, MACH creates `mach_events` to track
delivery. Crashes don't drop events; they replay on next boot.

- `.publishes` — outbound contracts: `.event` name, `.with` keys to pass
- `.events` — subscriber pipelines keyed by event name

```c
// publisher
config todos(){
  return (config){
    .name = "todos",
    .publishes = {
      {"todo_created", .with = {"user_id", "title"}},
      {"todo_deleted", .with = {"user_id", "todo_id"}}
    },
    .resources = {
      {"todos", "/todos",
        .post = {
          validate({"title", .validation = validate_not_empty}),
          query({"insert_todo", .db = "todos_db"}),
          emit("todo_created"),
          redirect("todos")
        }
      }
    }
  };
}

// subscriber: owns its OWN database (Rule 2)
config activity(){
  return (config){
    .name = "activity",
    .events = {
      {"todo_created", {
        query({.db = "activity_db",
          .query = "insert into activities(kind, user_id, ref) "
                   "values('created', {{user_id}}, {{title}});"})
      }}
    }
  };
}
```

### Task Pipelines

Named pipelines that run async on task reactors. Fire-and-forget. Defined
at module or root level. Triggered with `task("name")` or via `.cron`.
Tasks can enqueue more tasks.

Durable: `mach_tasks` checkpoints context after each step. Crash mid-task
→ resumes at the failed step.

- `.name` *(pos)* — identifier, called via `task("name")`
- `.accepts` — context keys to pull from caller into the task
- `.cron` — standard cron schedule (no caller required)
- *Steps* *(pos)* — pipeline body, second positional brace block

```c
.tasks = {
  // on-demand
  {"recount_todos", {
    query({.db = "todos_db",
      .query = "update users set todo_count = "
               "(select count(*) from todos where user_id = users.id) "
               "where id = {{user_id}};"})
  }, .accepts = {"user_id"}},

  // recurring
  {"daily_digest", {
    query({.db = "todos_db",
      .query = "insert into digest_reports(generated_at) values(now());"}),
    emit("digest_ready")
  }, .cron = "0 8 * * *"}
}
```

### Modules & Composition

Every app and module returns a `config`. Root `main.c` defines `mach()`;
modules define their own functions with any name. A module owns its
resources, **its own database** (Rule 2: one per domain), migrations,
templates, and event contracts. **Same-name conflicts: root wins.**
Modules communicate ONLY through pub/sub events.

- `.name` — module identifier
- `.modules` — other modules to compose (root or nested)

A module file:
```c
#include <mach.h>
#include <sqlite.h>

config blogs(){
  return (config){
    .name = "blogs",
    .resources = {
      {"blog", "/blogs/:id",
        .get = { /* validate → query → join → render */ }
      }
    },
    .databases = {{
      .engine     = sqlite_db,
      .name       = "blog_db",                       // ONE db for the blogs domain
      .connect    = "file:blogs.db?mode=rwc",
      .migrations = {                                // many tables, all in this db
        "CREATE TABLE blogs (id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT NOT NULL, content TEXT NOT NULL);",
        "CREATE TABLE comments (id INTEGER PRIMARY KEY AUTOINCREMENT, blog_id INTEGER NOT NULL REFERENCES blogs(id), body TEXT NOT NULL);"
      }
    }}
  };
}
```

Bring it in from `main.c`:
```c
#include <mach.h>
#include "blogs/blogs.c"

config mach(){ return (config){ .modules = {blogs, sqlite} }; }
```

Resource fields like `.url`, `.mime`, `.get` belong **inside** entries of
`.resources`, not at the top level of `config`.

Project layout:
```
├── todos/                # todos module — owns todos_db
│   ├── todos.c
│   ├── todos.mustache.html
│   ├── create_todos_table.sql
│   └── get_todos.sql
├── activity/             # activity module — owns activity_db
│   └── activity.c
├── static/               # root-level templates (not a module, no .c)
│   └── home.mustache.html
├── public/               # static files served directly
│   └── favicon.png
└── main.c
```

**Bundled modules** (add to `.modules`): `sqlite`, `postgres`, `mysql`,
`redis`, `duckdb`, `htmx`, `datastar`, `tailwind`, `session_auth`

**Module-provided steps.** Modules can ship step functions that plug into
pipelines like built-ins. `session_auth` provides:
- `session()` — attaches current session to context (sets `user_id`,
  etc.); no-op when unauthenticated
- `logged_in()` — guard, raises `http_not_authorized` if no session
- `login()`, `logout()`, `signup()` — for POST pipelines

Common as resource-level middleware via `.steps`:
```c
{"dashboard", "/dashboard", {session(), logged_in()},
  .get = { render("dashboard") }
}
```

### Static Files

Files in `public/` at project root are served directly. Reference with
`{{asset:filename}}`, which resolves to a content-checksummed URL with
immutable cache headers.

```
public/
├── favicon.png
├── logo.png
└── styles.css
```

```html
<link rel="icon" href="{{asset:favicon.png}}">
<link rel="stylesheet" href="{{asset:styles.css}}">
<script src="{{asset:app.js}}"></script>
```

### External Dependencies

Containerized dev environment; no local toolchain. Two ways to bring in
third-party C libraries, plus two memory bridges.

**`/vendor` directory** — drop in headers and `.so`/`.a`; auto-compiler
discovers, includes, and links them.
```
/vendor/
├── libsodium.h
└── libsodium.so
```

**Custom Dockerfile** — inherit from MACH base image, `apt-get` system
deps; reference from `compose.yml`.
```dockerfile
FROM mach:latest
RUN apt-get update && apt-get install -y libsodium-dev
```

**`allocate(bytes)`** — buffer from pipeline arena, reclaimed on request
completion.
```c
char *buf = allocate(256);
```

**`defer_free(ptr)`** — schedule cleanup for pointers from external libs
(`malloc`, etc.) when the arena is released.
```c
char *out = third_party_alloc(256);
defer_free(out);
```

---

## Architecture (brief)

- **Boot once.** `mach()` runs once at boot. The returned `config` is
  compiled into an execution graph with prepared queries and templates.
- **Multi-reactor.** Request reactors handle HTTP (one per CPU). Task
  reactors handle background jobs (one per CPU). Shared thread pool
  handles `exec()` and blocking I/O.
- **Memory.** Per-request arena allocators. No `malloc`/`free` in app
  code. Arena cleared on request end. Pipelines exceeding 5MB (default,
  configurable) abort with a 500.
- **Safety by default.** SQL injection prevented by parameter binding
  (Rule 4). XSS prevented by `render()` auto-escape; opt out with
  `{{raw:field}}`. CSRF prevented by `{{csrf:token}}` / `{{csrf:input}}`.
- **Tooling.** TUI editor with HMR/LSP/AI; `app_info`, `unit_tests`,
  `e2e_tests`, `app_debug`, `app_build` commands; OpenTelemetry on :4000.

---

## Final reminder — the rules a small model breaks most often

1. **No dot in `{{ }}`.** Every nested access is a section. (Rule 1)
2. **One database per domain, many tables.** Parent + child (project +
   tasks, blog + comments) is **one** domain, **one** db, **two
   migrations**. (Rule 2)
3. **Concurrent = ONE step, MANY items.** Even across databases. (Rule 3)
4. **Asset name OR `.query`, never both** in `query()`/`find()` items. (Rule 5)
5. **`join()` moves children.** After `join(tasks → project)`, `tasks`
   no longer exists at root. Open `{{#project}}` first. (Rule 1, Pattern C)

If you catch yourself writing `{{a.b}}`, declaring `projects_db` +
`tasks_db` for one domain, chaining three independent `query({...})`
steps, or rendering `{{#tasks}}` at root after a join — stop and fix it.