…limits

Add three operational environment overrides, resolved as env > config.toml
> default in both engines (agent-core and agent-core-v2), matching the
existing KIMI_IMAGE_MAX_EDGE_PX / KIMI_SUBAGENT_TIMEOUT_MS pattern:

- KIMI_LOOP_MAX_STEPS_PER_TURN overrides loop_control.max_steps_per_turn
- KIMI_LOOP_MAX_RETRIES_PER_STEP overrides loop_control.max_retries_per_step
- KIMI_CODE_BACKGROUND_MAX_RUNNING_TASKS overrides background.max_running_tasks

Invalid values are ignored and fall back to the config value. The v2 engine
resolves them through config section env bindings (effective-only, never
persisted); the v1 engine resolves them at the consumption point.

Environment overrides resolved into the effective config could be echoed
back through IConfigService.set/replace (e.g. GET then POST
/api/v1/config) and persisted into config.toml, outliving the env var.
This affected the pre-existing image / subagent / keep-alive bindings as
well as the new loop control and max-running-tasks bindings.

Extend ConfigStripEnv with a getEnv parameter and add a shared
stripEnvBoundFields helper: while a field's env var is set, writes
restore the field's raw on-disk value (or drop it) instead of persisting
an echoed env value; when unset, normal writes persist. Register it for
the loopControl, task/background, image, and subagent sections.

Also fix ConfigService.stripEnv looking up rawSnake by the camelCase
domain key; on-disk sections are keyed snake_case.

An invalid env value (e.g. KIMI_LOOP_MAX_STEPS_PER_TURN=abc) is ignored
on the read path but still marked the field env-owned on the write path,
so a config write for that field was silently dropped.
stripEnvBoundFields now derives the guard from the section's envBindings
and skips fields whose env value fails the binding's parse, so invalid
env values are ignored on both paths — and the duplicated field/env
descriptor list is gone.

Also drop function-level comments added beside helpers; agent-core-v2
keeps comments solely in the top-of-file block, so the strip semantics
now live in the config.ts / configService.ts headers.

auth.test.ts removed its temp home with a plain recursive rm, which races
late async writers in the server shutdown path and flakes with ENOTEMPTY
(seen on main CI and locally on main). Harden the cleanup with the same
maxRetries/retryDelay options sessions.test.ts already uses.

…tries

One feature entry (loop/background env overrides, both engines plus the
CLI) and one fix entry (env values persisting on writes and sticking
after degrade/unset, agent-core-v2 plus the CLI).

…s on get()

Two follow-ups from review:

- stripEnvBoundFields returned an empty object when every written field
  was env-owned, so a section with a non-empty default (e.g. subagent)
  stored raw = {} and the default stopped applying until the next
  reload. A fully stripped result now clears the raw section instead.
- get(domain) only recomputed env overlays for sections with env
  bindings, so domains written solely by a ConfigEffectiveOverlay
  (models / defaultModel from KIMI_MODEL_NAME) kept serving stale cached
  values after the env changed. get() now derives every non-memory
  domain from the fresh env-free base, matching getAll().

…verlay

The previous version imported the model env overlay to activate it, which
the CI runners failed to resolve from this test file (both tsgo and
vitest, while the same specifier resolves elsewhere — not reproducible
locally). An inline ConfigEffectiveOverlay double exercises the same
ConfigService contract with a tighter seam and no module dependency.

…rsist

Returning {} for a fully stripped write stored the empty object into the
raw layer while the TOML table survived via rawSnake, so the bases
diverged; a second echo write then saw an empty base, cleared the
section, and deleted the table — dropping unknown forward-compatible
fields. When nothing persistable remains, the write is now a no-op for
the section (the env-free base is kept as-is), and the section is
cleared only when the base is empty.

… persist

A strip may restore on-disk values from the unvalidated raw base (e.g.
an env-masked invalid field), smuggling them past the merge-time
validation into the stored config: the section would then fail the next
buildValidated pass, dropping accompanying valid edits from the runtime
while the invalid value stayed persisted. set() now revalidates the
stripped result — discarding the parse output so unknown fields survive
— and rejects the write instead, matching replace().