docs(#1544): add ADR 0040 for /fs- slash command prefix

docs/ADRs/0002-initial-fullsend-design.md

@@ -54,6 +54,12 @@ We propose adopting the following **reference workflow** as the mental model for
 
 **Slash commands (illustrative, configurable per repo):**
 
+> **Note:** The bare command names below (`/triage`, `/implement`,
+> `/review`) are illustrative. All production fullsend commands use the
+> `/fs-` prefix (e.g., `/fs-triage`, `/fs-code`, `/fs-review`) to avoid
+> collisions with other AI tools. See
+> [ADR 0042](0042-fs-prefix-for-slash-commands.md).
+
 - `/triage` — run or re-run triage on the issue **from scratch** (clears **`duplicate`** and other triage/ downstream labels at run start; **reopens** the issue if **`closed`**—see **When a triage run starts**)
 - `/implement` — hand off to the **Implementation** stage (implementation agent; expects **`ready-to-implement`** or forces with human ack — policy per repo)
 - `/review` — enqueue review swarm for current PR head

docs/ADRs/0042-fs-prefix-for-slash-commands.md

@@ -0,0 +1,78 @@
+---
+title: "42. Use /fs- prefix for all slash commands"
+status: Accepted
+relates_to:
+  - agent-architecture
+topics:
+  - slash-commands
+  - namespace
+  - ux
+---
+
+# 42. Use /fs- prefix for all slash commands
+
+Date: 2026-05-26
+
+## Status
+
+Accepted
+
+Supersedes the bare command examples in
+[ADR 0002](0002-initial-fullsend-design.md).
+
+## Context
+
+Multiple AI-powered tools respond to slash commands in GitHub issue and
+PR comments. GitHub Copilot uses `/fix` and `/review`; other bots use
+similar bare verbs. When fullsend agents listen for the same bare
+commands (e.g., `/triage`, `/implement`, `/review`), any of these tools
+may intercept the command, causing unintended side effects or ambiguous
+behavior.
+
+The original design document ([ADR 0002](0002-initial-fullsend-design.md))
+used bare commands as illustrative examples. As the ecosystem matured,
+the collision risk became concrete — Copilot and other tools already
+claim several of the same verbs.
+
+Two separate issues (#1473, #1477) were filed proposing workarounds for
+command collisions, both unaware that a namespacing decision had already
+been made but was recorded only in the
+[glossary](../glossary.md#slash-command). This ADR formalizes that
+decision so it is discoverable alongside other architectural choices.
+
+## Options
+
+### A. Bare commands (`/triage`, `/implement`, `/review`)
+
+- Pro: shorter to type, familiar syntax.
+- Con: collides with Copilot and other tools that claim the same verbs.
+
+### B. `/fs-` prefixed commands (`/fs-triage`, `/fs-code`, `/fs-review`)
+
+- Pro: unique namespace; no known collision with existing tools.
+- Pro: short enough to remain ergonomic.
+- Con: users must learn the prefix.
+
+### C. `/fullsend-` prefixed commands
+
+- Pro: unambiguous namespace.
+- Con: too verbose for frequent interactive use.
+
+## Decision
+
+All fullsend slash commands use the `/fs-` prefix
+(e.g., `/fs-triage`, `/fs-code`, `/fs-review`). The entry point's slash
+command parser must recognize only `/fs-`-prefixed commands and ignore
+bare verbs.
+
+## Consequences
+
+- Fullsend commands will not collide with Copilot, other AI bots, or
+  future GitHub-native slash commands.
+- Users and documentation must use the `/fs-` prefix; bare commands are
+  not recognized.
+- The glossary already reflects this convention. ADR 0002's illustrative
+  examples of bare commands (`/triage`, `/implement`, `/review`) are
+  superseded by this decision.
+- Agent prompt instructions, harness definitions, and dispatch
+  configuration that reference slash commands must use the `/fs-` form.