# Agent Note: credential boundaries, whole-snapshot requests, and atomic route registration

Status: implemented

English | [中文](2026-07-30-credential-boundaries-and-atomic-registration.zh.md)

> Scope: the third review round over the [request-level LLM configuration seam](2026-07-29-request-level-llm-config-credentials.md) — where a stored credential lives and who can read it, how one request's facts stay one generation, and how a route set changes without a window. Companion to the [settings write-path note](2026-07-30-settings-write-path-integrity.md), whose provider fixes this round applies to `credentials-local` and whose writer lock it promotes into `dsh-atomic-write`.

## Problem

Review found the credential path leaking across boundaries it had drawn. The shipped surfaces hoisted `$DSH_HOME/.env` into `process.env` before cordis booted, so on the next run `credentials-local` classified every key it had stored itself as a read-only ambient launch override: `describe()` reported `source: 'env'` with `writable: false`, `set`/`unset` rejected as shadowed, and a key stored from the web page or TUI became unrotatable and undeletable while the adapter kept using the value captured at launch. The store's own write path repeated the settings-local defects that same review round fixed (two independent chains, whole-file render from a stale cache), plus editor bugs of its own: a physical line inside another key's quoted multi-line value read as an assignment, CRLF endings degraded to LF, a multi-line entry reported `writable: true` while `set` always threw, and `credentials/updated` was emitted bare after the commit, so one broken observer made a durable write look failed. On the read side, the file's `0600` mode stops other OS users but not the model, whose bash and filesystem tools run as the same user.

Two request-path defects sat beside them. DeepSeek resolved connection and credential facts independently, so a settings generation the resolver rejected could still pair its credential choice with the previous generation's endpoint. pi-ai handed the SDK `undefined` when a configured `apiKeyEnv` resolved to nothing, letting pi-ai's own environment discovery authenticate with an unrelated provider key — another tenant, silently billed. And its route swap disposed the old registration before creating the new one: a route another adapter owned dropped every existing route, after which the facts cache could equal the registry's, so restoring the working configuration never re-applied.

## Decision

**The credential document belongs to the credential provider alone.** No surface loads it into `process.env`. It was `$DSH_HOME/.env` here; the [credentials document split](2026-08-04-credentials-yaml-and-user-environment-layer.md) later moved it to `$DSH_HOME/.credentials.yaml`, so today it is the old path that is loaded — as the user's ordinary environment layer, holding no provider-managed secret. The genuine launch environment and the invoking directory's `.env` (loaded by the bin) stay the read-only ambient layer, so a composition without the provider resolves keys exactly as before, while a stored key stays file-sourced and writable across restarts — proven by a real restart in the loader composition rather than by a unit assertion about `describe()`.

**The stored credential has no boundary against the model, and the READMEs say so.** `0600` under a `0700` directory stops other OS users; the model's bash and filesystem tools run as that same user, and the shipped default confines nothing. What the harness does hold to is narrower and stated as exactly that: no surface hoists the document into `process.env`, and the model is never handed a resolved path to it, so reaching the value takes a deliberate read of a path it was not given. An OS-keychain provider — a store the model's processes cannot read at all — is recorded as the real answer rather than implied by a partial one.

**One request, one generation.** DeepSeek's resolved snapshot carries the credential reference beside the endpoint, and `resolveApiKey` receives that snapshot instead of re-reading configuration. A rejected generation now contributes nothing at all. pi-ai defers to provider-native discovery only for a profile naming no credential; a configured reference that misses fails with `MISSING_CREDENTIAL` naming the route and the reference. The boot-time credential probe is deleted: it could run before the credentials service mounted and reported every failure as a missing key, while the first request already gives the accurate error.

**Route replacement is a registry operation, not a caller sequence.** `registerAdapter` returns a handle carrying `replace(providers)`: the candidate set is validated in full first (conflicts, names, provider metadata), then swapped in one synchronous section. A refused replacement leaves the previous routes registered and serving, and the caller's facts cache only advances after the registry actually holds the new set, so reverting to a working configuration re-applies. pi-ai's registration facts are sorted by provider, so a settings document that merely reorders its keys is no longer a route change.

**Contained publication for committed credential writes.** `Credentials.notifyUpdated` fans `credentials/updated` out one listener at a time; sync throws and async rejections are logged without changing the committed operation's outcome, and `INVARIANT`-coded failures rethrow after every listener ran — the same shape the settings seam uses for `settings/updated`. `installSettingsSection`'s cleanup now distinguishes its two triggers: a provider detaching still falls back to the composition entry and re-derives, while the consumer's own unload returns immediately instead of re-registering routes during teardown.

## Alternatives considered

- **A sandbox read-denial naming `$DSH_HOME/.env`** — implemented as a `readDenyPaths` policy field (a trailing SBPL `deny file-read* file-write*`, a `/dev/null` bwrap bind) and withdrawn on its own evidence. bwrap must create that bind's mount point inside a tree its profile has already made read-only, so it refuses the entire confinement whenever the parent directory is absent — every host that has not stored a credential yet, including a fresh install; Landlock cannot subtract from its own `/` read grant, so every confined call would report `partial` for a file it never hid. A protection that breaks confinement where it works and misreports it where it does not is worse than a documented absence. Denying the whole harness home was rejected earlier for a separate reason: it also covers `sessions/`, and `DSH_SESSION_JSONL` is a documented model-visible capability.
- **Removing `DSH_HOME` from the model's bash environment** — considered as defense in depth and rejected as theater with a real cost: the default home is a documented convention the agent can reconstruct, while the variable is how legitimate tooling finds harness state. There is no boundary here for it to complement; hiding the pointer would only make the absence harder to see.
- **Shipping the OS-keychain provider in this round** — it is the only design where the model's processes genuinely cannot read the secret, and it is a sibling package with three platform backends. Sizing it against the rest of this review round would have delayed every other fix; it is recorded as the deferred answer, not as a maybe.
- **A `replaceRegistration(previous, next)` service method** — the review's shape, but it makes the caller carry the previous handle and lets it pass a mismatched one. Hanging `replace` on the registration handle makes ownership structural: only the registration that holds routes can replace them.

## Consequences

`update()`-adjacent behavior gained documented failure modes: a credential write can now fail on the lock deadline or on an unparsable on-disk document, and `describe()` reports `writable: false` for multi-line entries it will not rewrite. `LlmAdapter` registrants keep working unchanged (the handle is still callable as the disposer), and `DeepSeekConnectionOptions` gained credential fields, so a programmatic constructor of the adapter must supply `apiKeyEnv`. Deferred: the OS-keychain credential provider, and per-value revision checks for two writers editing one reference (last-write-wins remains the documented resolution).
