Prune the description to the declared operations at packing time

[haruotsu]

gete archive now prunes the OpenAPI description to the declared
operations, and validate reports a path template placeholder no path
parameter declares.

Why gete does the cutting

A published description holds far more than an agent declares, and
operations being required already keeps the runtime honest — the model is
offered only what was declared however much the file holds. The tempting
next step is to keep a hand-trimmed copy of the description in the repo,
and that step breaks quietly, in at least two ways:

1. flattening a $ref drops the parameters it carried;
2. dropping a path item's own parameters entry drops the same parameters
   another way — OpenAPI lets path-level parameters live outside the
   operation, and by reference at that.

Both mistakes validate cleanly: the operations are still there, they just
can no longer say which record they address. Nothing notices until someone
counts the arguments on the deployed tools. If pruning is worth doing, the
only safe place is where read_operations already knows what a path item
contributes and where every reference leads.

What archive packs now

• The declared operations ride with their whole path item — path-level
  parameters included — so nothing an operation inherits is lost.
• Every node the kept parts reference is grafted at its original JSON
  pointer, transitively, so $ref keeps resolving; unreferenced
  components stay behind. A pointer into paths is deliberately not
  grafted — it would re-select what pruning just left out.
• The published servers stay behind too; nothing ever reads them
  (request URLs come from the connection's base_url).
• A file two blocks share (a read block and a write block, typically)
  keeps the union of their operations.
• The bytes are deterministic, as everything in an archive must be —
  Terraform decides deployment by the archive hash.
• The vendor's original stays untouched in the repo; validate keeps
  running against it. Only what travels — and what a cold start reads —
  shrinks.

The validate rule

For descriptions gete did not produce (hand-written or hand-trimmed),
validate now reports the resulting shape early and by name:

operations: 'ShowTicket' has {ticket_id} in its path, and no path parameter declares it

A runtime-equivalence test holds the two paths together: the tools built
from a pruned description carry declarations identical to those built from
the whole one.