Record the inputs a run actually starts from, not only the ones passed

A run submitted without explicit inputs recorded `params = {}`: Port
initials filled the values at node level and were never written back, so an
exported row had a blank `param.*` cell and the runs listing could not tell
a run that took every default from one submitted with those same numbers.
Declared initials are now folded in at submit, explicit values winning, and
the run-level seed still wins over a declared one.

`params_digest` is computed over the resolved values, so it changes shape
once: a run recorded before this does not dedupe against a newer identical
submit, and its stage-cache entries miss once.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019Hra4ndWMCLU5F3KjUuVAc

backend/fluksio/flow/runs.py

@@ -846,6 +846,20 @@ class RunService:
         # reference a python caller would have passed and every later reader —
         # the digest, the cache, the run detail — sees one spelling.
         params = resolve_references(flow, params, self._artifacts)
+        # What the run actually starts from, not only what was passed: an input
+        # left out takes its declared value, and a row that records `{}` cannot
+        # say which. Folded literally — an initial is a value from the
+        # definition, never a reference to resolve. The run-level seed still
+        # wins over a declared one, the way `seed_values` has it.
+        params = {
+            **{
+                declared.spec.name: declared.initial
+                for declared in flow.inputs
+                if declared.initial is not None
+                and not (declared.spec.name == "seed" and seed is not None)
+            },
+            **params,
+        }
         # Checked here rather than in the driver: a caller who mistyped a
         # parameter should be told now, not by a run that fails in a minute.
         seed_values(flow, params, seed)