feat(adapters): add capability flags to ServerAdapterModule (#3540)

## Thinking Path

> - Paperclip orchestrates AI agents via adapters (`claude_local`,
`codex_local`, etc.)
> - Each adapter type has different capabilities — instructions bundles,
skill materialization, local JWT — but these were gated by 5 hardcoded
type lists scattered across server routes and UI components
> - External adapter plugins (e.g. a future `opencode_k8s`) cannot add
themselves to those hardcoded lists without patching Paperclip source
> - The existing `supportsLocalAgentJwt` field on `ServerAdapterModule`
proves the right pattern already exists; it just wasn't applied to the
other capability gates
> - This pull request replaces the 4 remaining hardcoded lists with
declarative capability flags on `ServerAdapterModule`, exposed through
the adapter listing API
> - The benefit is that external adapter plugins can now declare their
own capabilities without any changes to Paperclip source code

## What Changed

- **`packages/adapter-utils/src/types.ts`** — added optional capability
fields to `ServerAdapterModule`: `supportsInstructionsBundle`,
`instructionsPathKey`, `requiresMaterializedRuntimeSkills`
- **`server/src/routes/agents.ts`** — replaced
`DEFAULT_MANAGED_INSTRUCTIONS_ADAPTER_TYPES` and
`ADAPTERS_REQUIRING_MATERIALIZED_RUNTIME_SKILLS` hardcoded sets with
capability-aware helper functions that fall back to the legacy sets for
adapters that don't set flags
- **`server/src/routes/adapters.ts`** — `GET /api/adapters` now includes
a `capabilities` object per adapter (all four flags + derived
`supportsSkills`)
- **`server/src/adapters/registry.ts`** — all built-in adapters
(`claude_local`, `codex_local`, `process`, `cursor`) now declare flags
explicitly
- **`ui/src/adapters/use-adapter-capabilities.ts`** — new hook that
fetches adapter capabilities from the API
- **`ui/src/pages/AgentDetail.tsx`** — replaced hardcoded `isLocal`
allowlist with `capabilities.supportsInstructionsBundle` from the API
- **`ui/src/components/AgentConfigForm.tsx`** /
**`OnboardingWizard.tsx`** — replaced `NONLOCAL_TYPES` denylist with
capability-based checks
- **`server/src/__tests__/adapter-registry.test.ts`** /
**`adapter-routes.test.ts`** — tests covering flag exposure,
undefined-when-unset, and per-adapter values
- **`docs/adapters/creating-an-adapter.md`** — new "Capability Flags"
section documenting all flags and an example for external plugin authors

## Verification

- Run `pnpm test --filter=@paperclip/server -- adapter-registry
adapter-routes` — all new tests pass
- Run `pnpm test --filter=@paperclip/adapter-utils` — existing tests
still pass
- Spin up dev server, open an agent with `claude_local` type —
instructions bundle tab still visible
- Create/open an agent with a non-local type — instructions bundle tab
still hidden
- Call `GET /api/adapters` and verify each adapter includes a
`capabilities` object with the correct flags

## Risks

- **Low risk overall** — all new flags are optional with
backwards-compatible fallbacks to the existing hardcoded sets; no
adapter behaviour changes unless a flag is explicitly set
- Adapters that do not declare flags continue to use the legacy lists,
so there is no regression risk for built-in adapters
- The UI capability hook adds one API call to AgentDetail mount; this is
a pre-existing endpoint, so no new latency path is introduced

## Model Used

- Provider: Anthropic
- Model: Claude Sonnet 4.6 (`claude-sonnet-4-6`)
- Context: 200k token context window
- Mode: Agentic tool use (code editing, bash, grep, file reads)

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Pawla Abdul (Bot) <pawla@groombook.dev>
Co-authored-by: Paperclip <noreply@paperclip.ing>

docs/adapters/creating-an-adapter.md

@@ -203,6 +203,43 @@ export const sessionCodec: AdapterSessionCodec = {
 };
 ```
 
+## Capability Flags
+
+Adapters can declare what "local" capabilities they support by setting optional fields on the `ServerAdapterModule`. The server and UI use these flags to decide which features to enable for agents using the adapter (instructions bundle editor, skills sync, JWT auth, etc.).
+
+| Flag | Type | Default | What it controls |
+|------|------|---------|------------------|
+| `supportsLocalAgentJwt` | `boolean` | `false` | Whether heartbeat generates a local JWT for the agent |
+| `supportsInstructionsBundle` | `boolean` | `false` | Managed instructions bundle (AGENTS.md) — server-side resolution + UI editor |
+| `instructionsPathKey` | `string` | `"instructionsFilePath"` | The `adapterConfig` key that holds the instructions file path |
+| `requiresMaterializedRuntimeSkills` | `boolean` | `false` | Whether runtime skill entries must be written to disk before execution |
+
+These flags are exposed via `GET /api/adapters` in a `capabilities` object, along with a derived `supportsSkills` flag (true when `listSkills` or `syncSkills` is defined).
+
+### Example
+
+```ts
+export function createServerAdapter(): ServerAdapterModule {
+  return {
+    type: "my_k8s_adapter",
+    execute: myExecute,
+    testEnvironment: myTestEnvironment,
+    listSkills: myListSkills,
+    syncSkills: mySyncSkills,
+
+    // Capability flags
+    supportsLocalAgentJwt: true,
+    supportsInstructionsBundle: true,
+    instructionsPathKey: "instructionsFilePath",
+    requiresMaterializedRuntimeSkills: true,
+  };
+}
+```
+
+With these flags set, the Paperclip UI will automatically show the instructions bundle editor, skills management tab, and working directory field for agents using this adapter — no Paperclip source changes required.
+
+If capability flags are not set, the server falls back to legacy hardcoded lists for built-in adapter types. External adapters that omit the flags will default to `false` for all capabilities.
+
 ## Skills Injection
 
 Make Paperclip skills discoverable to your agent runtime without writing to the agent's working directory: