feat(aura-cli, aura-engine): graph introspect --taps — positive declared-tap discovery

Harvest sweep, batch 3 of 6 (first half).

Composite::declared_taps() walks the blueprint depth-first collecting
(tap name, source wire, column kind), names bare at every depth —
mirroring inline_composite's hoist, where a tap's name IS the flat
graph's load-bearing identifier — and bounds-total over invalid wires
(compile's validate_wiring stays the real gate). The CLI view loads
like --params (FILE gates the authored root name, a content id does
not), prints one 'name  node.field  Kind' row per tap, and renders the
tap-less case as a stderr note with empty stdout, exit 0.

Closes the recovery-only discovery loop: since #333 the only way to
learn a blueprint's declared tap names was provoking the undeclared-tap
refusal roster.

closes #337

crates/aura-cli/src/graph_construct.rs

@@ -589,10 +589,11 @@ fn introspect_registered(env: &aura_runner::project::Env) -> Result<String, Stri
 }
 
 /// `aura graph introspect`: dispatch the read-only queries. Exactly one of
-/// `--vocabulary` / `--node <T>` / `--unwired` / `--params <FILE|ID>` / the id
-/// group must be set; zero or more than one is the usage error (exit 2). The id
-/// group is `--content-id [FILE]` and/or `--identity-id` — the two id flags may
-/// combine (one build, both ids, content id first).
+/// `--vocabulary` / `--node <T>` / `--unwired` / `--params <FILE|ID>` /
+/// `--taps <FILE|ID>` / the id group must be set; zero or more than one is the
+/// usage error (exit 2). The id group is `--content-id [FILE]` and/or
+/// `--identity-id` — the two id flags may combine (one build, both ids,
+/// content id first).
 pub fn introspect_cmd(cmd: crate::GraphIntrospectCmd, env: &aura_runner::project::Env) {
     let count = cmd.vocabulary as usize
         + cmd.node.is_some() as usize
@@ -600,10 +601,11 @@ pub fn introspect_cmd(cmd: crate::GraphIntrospectCmd, env: &aura_runner::project
         + cmd.folds as usize
         + cmd.registered as usize
         + cmd.params.is_some() as usize
+        + cmd.taps.is_some() as usize
         + (cmd.content_id.is_some() || cmd.identity_id) as usize;
     if count != 1 {
         eprintln!(
-            "aura: Usage: aura graph introspect --vocabulary | --node <T> | --unwired | --folds | --registered | --params <FILE|ID> | --content-id [FILE] | --identity-id (the two id flags may be combined)"
+            "aura: Usage: aura graph introspect --vocabulary | --node <T> | --unwired | --folds | --registered | --params <FILE|ID> | --taps <FILE|ID> | --content-id [FILE] | --identity-id (the two id flags may be combined)"
         );
         std::process::exit(2);
     }
@@ -675,6 +677,18 @@ pub fn introspect_cmd(cmd: crate::GraphIntrospectCmd, env: &aura_runner::project
                 std::process::exit(1);
             }
         }
+    } else if let Some(target) = cmd.taps.as_deref() {
+        // --taps <FILE|ID> (#337): the positive declared-tap discovery view —
+        // #333 shipped only the refusal roster (`bind_tap_plan`'s
+        // `UnknownTap`), so provoking that refusal was the only way to learn
+        // a blueprint's declared tap names.
+        match taps_lines(target, env) {
+            Ok(s) => print!("{s}"),
+            Err(m) => {
+                eprintln!("aura: {m}");
+                std::process::exit(1);
+            }
+        }
     } else {
         // --content-id [FILE] / --identity-id (combinable): one build, then each
         // requested id on its own line, content id first. With a FILE value the
@@ -997,6 +1011,31 @@ fn params_lines(target: &str, env: &aura_runner::project::Env) -> Result<String,
     Ok(out)
 }
 
+/// `aura graph introspect --taps <FILE|ID>` (#337): one row per declared tap
+/// — `<name>  <node>.<field>  <kind:?>` — the positive discovery view #333's
+/// refusal roster (`bind_tap_plan`'s `UnknownTap`) deliberately deferred:
+/// before this, the only way to learn a blueprint's declared tap names was
+/// provoking that refusal. Loads exactly like `--params` (FILE gates the
+/// authored root name, a store content id does not, C29). A tap-less
+/// blueprint prints nothing to stdout — nothing was declared to list — plus a
+/// stderr note (the `bind_tap_plan` unbound-this-run note's own "aura: note:"
+/// convention), exit 0: a listing, not a fault.
+fn taps_lines(target: &str, env: &aura_runner::project::Env) -> Result<String, String> {
+    use std::fmt::Write as _;
+    let (text, is_file) = resolve_blueprint_text(target, env)?;
+    let composite = if is_file { composite_from_authored_text(&text, env)? } else { composite_from_any(&text, env)? };
+    let taps = composite.declared_taps();
+    if taps.is_empty() {
+        eprintln!("aura: note: {target} declares no taps");
+        return Ok(String::new());
+    }
+    let mut out = String::new();
+    for (name, wire, kind) in taps {
+        let _ = writeln!(out, "{name}  {wire}  {kind:?}");
+    }
+    Ok(out)
+}
+
 /// `aura graph register <blueprint.json> [--name <label>]` (#196, `--name`
 /// #317): parse the blueprint through the project vocabulary, canonicalize,
 /// content-address, and store — the `process register` pattern, printing

crates/aura-cli/src/main.rs

@@ -911,6 +911,12 @@ struct GraphIntrospectCmd {
     /// name:kind line per open param. FILE path or 64-hex store content id (#196).
     #[arg(long, value_name = "FILE|ID")]
     params: Option<String>,
+    /// List a blueprint's declared taps, one row per tap (#337): name, source
+    /// wire (`node.field`), column kind. FILE path or 64-hex store content id
+    /// (#196), like `--params`. The positive twin of the undeclared-tap
+    /// refusal roster (#333).
+    #[arg(long, value_name = "FILE|ID")]
+    taps: Option<String>,
 }
 
 #[derive(Args)]