fix(aura-cli, docs): fieldtest bugs — a refusal that misdirects, a handle denied, a stale signature

RED-first fixes for the three bugs the source-blind field test caught. Two
are the same failure the whole cycle keeps circling: prose that tells a
caller something the code does not do.

- The chart not-found refusal prescribed `aura exec --tap <NODE.FIELD>=<FOLD>`.
  The selector takes a declared tap NAME, so following the refusal verbatim
  earns a second refusal ("the tap plan names 'sub.value', but the blueprint
  declares no such tap"), and the flag is not needed at all — a plain run
  records every declared tap. This sentence predates the cycle and was carried
  over verbatim while the rest of the refusal was corrected; the field test
  ran it as written, which is exactly why it ran it.
- `aura measure ic <family-handle>` answered "no recorded run '…' under
  runs/traces" for a handle that IS recorded — the value the campaign run
  printed, that `chart` renders, whose directory exists. A family holds
  members rather than one series, so IC is measured over a member. The
  refusal now says that and lists the member keys, which also closes the
  friction that nothing on any text surface prints them: reaching a member
  previously meant the very `ls runs/traces/` this cycle set out to retire.
- C28's #297 note still gave the entry points' signature as the retired
  `(_, Vec<String>)` pair in the present tense, contradicting C27 one contract
  over. The close commit claimed lockstep; this makes it true.

Both code fixes have tests that fail without them. The field test also found
four friction items and two spec gaps, filed rather than fixed here.

refs #309

docs/design/contracts/c28-stratification.md

@@ -173,8 +173,10 @@ the single-run verb paths (`member.rs` ×8, `measure.rs` ×5, `translate.rs`
 ×1 — the "~24" this paragraph used to cite predates the #319 dual-grammar
 retirement and never updated in lockstep) are now `RunnerError { exit_code,
 message }` constructors threaded through a fallible chain; the two entry
-points, `run_signal_r` and `run_measurement`, return
-`Result<(_, Vec<String>), RunnerError>`, and the CLI's `exec_blueprint_leg`
+points, `run_signal_r` and `run_measurement`, return a fallible outcome
+carrying the report beside the per-invocation values the shell renders
+(`Result<RunOutcome<_>, RunnerError>` since #309 widened the original
+`(_, Vec<String>)` pair), and the CLI's `exec_blueprint_leg`
 remaps via one shared `exit_on_runner_error` helper (the `dispatch_reproduce`
 pattern). The one hole in "a sweep worker never process-exits" — `cost_knob`,
 reachable from `run_blueprint_member` — is closed the same cycle: the