refactor(common): centralize HealthResponse status strings as pub constants

[geoffjay]

refactor(common): centralize HealthResponse status strings as pub constants

refactor(common): centralize HealthResponse status strings as pub constants (closes #721)

[geoffjay]

This change is part of the following stack:

• refactor(common): centralize HealthResponse status strings as pub constants #737 ◀

_{Change managed by git-spice.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.66%. Comparing base (a5867f0) to head (067a737).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #737   +/-   ##
=======================================
  Coverage   55.66%   55.66%           
=======================================
  Files         126      126           
  Lines       13759    13760    +1     
=======================================
+ Hits         7659     7660    +1     
  Misses       6100     6100           

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[geoffjay]

Review: refactor(common): centralize HealthResponse status strings as pub constants

Stack position: issue-721 is directly on main with no parent PR
dependency, but git-spice reports (needs restack) — the branch is behind
main and must be rebased before the conductor can merge it.

---

Code quality: approved

The change is correct, focused, and complete within its stated scope.

Constants — STATUS_OK = "ok" and STATUS_DEGRADED = "degraded" are
exact replacements for the literals they supersede. Module-level placement
(rather than associated constants on impl HealthResponse) is a valid and
idiomatic choice; callers import them as agentd_common::types::STATUS_OK.

Three use sites updated — ok(), degraded(), and is_healthy() in
types.rs all use the constants consistently. No fourth call site was missed.

pub visibility — correct per the architect guidance stored in memory: downstream
crates (CLI, integration tests) can now import the constants instead of
hardcoding the string. The change is additive — existing callers comparing
against "ok" in JSON assertions are unaffected and can migrate
opportunistically.

No behaviour change — the string values are identical; existing tests pass
without modification.

Scope — single file, single concern, no unrelated changes.

---

Observation (no action required)

grep across the codebase shows several downstream sites still using "ok"
and "degraded" literals directly against HealthResponse.status (e.g.,
crates/memory/src/api.rs, crates/monitor/src/api.rs). These can migrate
to STATUS_OK / STATUS_DEGRADED in a follow-up, but are out of scope here
and not broken.

---

Action required before merge

Rebase onto main:

git-spice branch restack
git-spice branch submit

Once restacked, add merge-queue to trigger the conductor.