runtime: read the fixture and process overrides from InitRequest, not only Start #71

Agent-side half of codefly-dev/core#526.

pkg/runtime/runtime.go consumes both values only inside Start:

s.EnvironmentVariables.SetFixture(req.Fixture)
s.EnvironmentVariables.AddOverrides(req.GetOverrides())

A service under test is not always started: a TEST_DEPENDENCY_MODE_START_DEPENDENCIES policy replaces its RuntimeStart with a no-op sequencing barrier and NONE skips Start entirely. Under the two modes a dependency-backed suite actually uses, the service observes no CODEFLY__FIXTURE, no CODEFLY__API_CONSUMES and no federation registration secrets — the suite runs green against a composition that was never wired. The CLI populates both fields on every InitRequest (codefly-dev/cli#689).

Change

In Runtime.Init, alongside the runtime context it already records:

s.Runtime.SetFixtureFromInit(req.GetFixture())
s.Runtime.SetOverridesFromInit(req.GetOverrides())

and switch the existing Start calls to the non-authoritative twins SetFixtureFromStart / SetOverridesFromStart, so a barrier Start carrying nothing cannot clear what Init recorded, and a Start repeating a key cannot leave the process holding two entries for it (AddOverrides appends unconditionally). Precedence is first-non-empty, Init before Start; both pairs are nil-safe and ignore an empty selection.

The contract is documented in core docs/agent-development.md, under Runtime → Fixture and process overrides.

Gate

Needs a core pin carrying core#520 and core#525. No tag has them yet: v0.3.31 predates both. codefly-dev/core#527 bumps version/info.codefly.yaml to 0.3.32, which cuts that tag on merge — pin v0.3.32 (or newer) first.