refactor: extract validate_startable from start.rs handle

[mukeshblackhat]

Summary

• Extracted validate_startable — pure function with an exhaustive match on all InstanceStatus variants
• Updated handle to call the helper instead of inline if chains
• Added 10 unit tests covering every InstanceStatus variant
• #[allow(clippy::cognitive_complexity, clippy::too_many_lines)] kept on handle — still triggers both lints after extraction (follow-up ticket)

What was there before

handle (line 48) had status validation inlined as if chains at lines 64-79. Two conditions: one rejecting Running/CheckedOut ("already running"), another rejecting Provisioning/Assigning/Starting/Stopping ("currently..."). Everything else fell through as startable.

What changed

Single file: coast-daemon/src/handlers/start.rs

Extracted function:

fn validate_startable(status: &InstanceStatus, name: &str) -> Result<()>

Status	Result	Reason
Stopped, Idle, Enqueued, Unassigning	Ok(())	Startable — preserves original fall-through behavior
Running, CheckedOut	Error "already running"	Same as before
Provisioning, Assigning, Starting, Stopping	Error "currently..."	Same as before

Follows the same pattern as validate_stoppable in stop.rs (PR #126).

Behavior preservation

The original code only explicitly rejected Running, CheckedOut, and the 4 transitional states. Stopped, Idle, Enqueued, and Unassigning all fell through as startable. Our exhaustive match preserves this exactly — no new rejections added.

All 3 callers of start::handle (mod.rs:550, mod.rs:570, rerun_extractors.rs:327) handle Ok/Err generically and are unaffected.

Test plan

Run new tests

# 14 tests pass (4 existing + 10 new)
cargo test -p coast-daemon -- start::tests

Run lint and full tests

make lint    # zero warnings
make test    # all pass

Verify no regressions in related handlers

# Archive depends on start/stop — verify it still works
cargo test -p coast-daemon -- archive

# Rerun extractors calls start::handle for Stopped instances
cargo test -p coast-daemon -- rerun_extractors

Closes #133

[jamiesunderland]

but we still need to remove this to confirm if it works

[mukeshblackhat]

even if we separate them as well, we will not be able to remove the complete
#[allow(clippy::cognitive_complexity, clippy::too_many_lines)]
still the lines will be over the limit and complexity

these will be the hardest one to remove as they are asycn and
Load image, Compose up and Wait for health checks
they are interconnected and depended as well so trickiest part here.

[jamiesunderland]

Yeah, let's try that. Make sure to add new tests for new code introduced. I'll give it a test after.

[mukeshblackhat]

Phase 2 & 3: Extract remaining phases from handle, remove #[allow]

Three commits pushed that complete the extraction work.

What changed

Extracted 8 helpers from handle:

• verify_inner_daemon_health — Runs docker info with 10s timeout, normalizes socket permissions
• build_workspace_mount_command — Pure string construction for mount command
• start_bare_services_if_present — Checks supervisor dir, starts bare services
• reapply_workspace_mount — Computes mount source, builds symlink fix, execs mount
• setup_shared_services — Builds routing targets, plans + ensures proxies
• run_compose_and_wait_for_health — Compose up + polls health until ready
• backfill_build_id — Reads latest symlink, persists build ID in DB
• run_docker_operations — Orchestrates all Docker phase steps

#[allow(clippy::cognitive_complexity, clippy::too_many_lines)] removed — both lints now pass without suppression.

22 new tests added (46 total in the module, up from 14).

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Why files other than start.rs were touched

coast-daemon/Cargo.toml
Added async-trait to [dev-dependencies]. Needed because MockRuntime in our tests implements the Runtime trait which uses #[async_trait]. This is a dev-only dependency — no runtime impact.

coast-daemon/src/handlers/run/service_start.rs
Changed compose_ps_output_is_ready from fn to pub(crate) fn. The inline compose health check in start.rs was duplicating the exact same logic. Instead of copying it, we reuse the existing tested
function. DRY fix.

coast-daemon/src/handlers/run/mod.rs
Added pub(crate) use service_start::compose_ps_output_is_ready; re-export so start.rs can access it.

Cargo.lock
Auto-updated from the async-trait addition.

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Why MockRuntime and &dyn Runtime

The extracted helpers need Docker operations (exec_in_coast). To test them without a real Docker daemon, we use &dyn Runtime (the trait from coast-docker/src/runtime.rs) instead of &bollard::Docker. This
lets us pass a MockRuntime in tests that returns scripted ExecResult values.

This is the same pattern already used in coast-docker/src/container.rs — ContainerManager<R: Runtime> with a MockRuntime in its test module.

We also changed normalize_inner_docker_socket_permissions from &bollard::Docker to &dyn Runtime for the same reason. Note: provision.rs has its own separate private copy of that function — it was not
touched.

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No public API changes

• pub async fn handle signature unchanged — same 3 params, same return type
• All 3 callers (mod.rs:550, mod.rs:570, rerun_extractors.rs:327) unaffected
• All new functions are private to start.rs