fix: tighten project instruction path handling

docs/architecture.md

@@ -22,7 +22,7 @@ For a catalog of the **data structures** this architecture moves around — the
 │  future plugins: hooks, compaction, sandbox, UI, MCP…        │
 ├─────────────────────────────────────────────────────────────┤
 │  @deepseek-ai/dsh-agent-loop      (the ONE concrete plugin)  │
-│  @deepseek-ai/dsh-project-instructions (AGENTS.md loader)     │
+│  @deepseek-ai/dsh-project-instructions (AGENTS.md loader)    │
 │  @deepseek-ai/dsh-bash-local      (bash impl)                │
 │  @deepseek-ai/dsh-tool-bash       (bash tool schemas)        │
 │  @deepseek-ai/dsh-session-persistence-jsonl (persistence impl)│
@@ -97,7 +97,7 @@ Replay/fork = `ctx.sessions.create(id, { seed: seedEvents })`. Trace/telemetry =
 
 Plugins contribute `PromptSection`s (named, ordered, static or computed) and tool-schema providers. `assemble()` returns a `PromptAssembly { sections, tools }` through the `system-prompt/assemble` waterfall.
 
-Prompt/context extension plugins that shape model inputs without owning a core service live under `packages/prompt/`. `dsh-project-instructions` is the reference case: it is semantically prompt/context assembly, but it uses the per-agent `agent/request` seam instead of a global `ctx.systemPrompt.section()` so concurrent sessions with different cwd values stay isolated.
+Prompt/context extension plugins that shape model inputs without owning a core service live under `packages/prompt/`. `dsh-project-instructions` is the reference case: it is semantically prompt/context assembly, but it uses the per-agent `agent/request` seam instead of a global `ctx.systemPrompt.section()` so concurrent sessions with different cwd values stay isolated. Shared filesystem path conventions such as the default DSH home live in the low-level `dsh-paths` utility package rather than in the prompt plugin.
 
 Tool schemas are deliberately **part of the assembly**: "what the model is told it can do" is one coherent thing managed here, even though adapters transmit schemas as the wire-level `tools` field rather than prompt text.
 

docs/module-graph.md

@@ -28,6 +28,7 @@ graph TD
   invariants --> session
   project-instructions --> agent
   project-instructions --> llm
+  project-instructions --> paths
   session-persistence-jsonl --> session
   session-persistence-jsonl --> session-persistence
   session-persistence-sqlite --> session
@@ -100,6 +101,7 @@ graph TD
 | Package | Depends on |
 | --- | --- |
 | `brand` | — |
+| `paths` | — |
 | `bash` | `brand` |
 | `llm` | `brand` |
 | `bash-local` | `bash` |
@@ -112,7 +114,7 @@ graph TD
 | `llm-replay` | `llm`, `session` |
 | `session-persistence` | `session` |
 | `invariants` | `agent`, `llm`, `session` |
-| `project-instructions` | `agent`, `llm` |
+| `project-instructions` | `agent`, `llm`, `paths` |
 | `session-persistence-jsonl` | `session`, `session-persistence` |
 | `session-persistence-sqlite` | `session`, `session-persistence` |
 | `tools` | `agent`, `llm`, `system-prompt` |

docs/rfc/implemented/feature/2026-06-24-project-instruction-files.md

@@ -12,7 +12,7 @@ The non-obvious constraint is multi-session cwd. `dsh-system-prompt` sections ar
 
 ## Proposal
 
-Add a new plugin package `packages/prompt/project-instructions` (`@deepseek-ai/dsh-project-instructions`). It is a single-purpose prompt/context extension plugin, not an interface/implementation/consumer capability seam: there is no swappable backend, only filesystem discovery plus per-request context injection. It depends on interface packages only (`dsh-agent` and `dsh-llm`) and consumes the existing `agent/request` waterfall.
+Add a new plugin package `packages/prompt/project-instructions` (`@deepseek-ai/dsh-project-instructions`). It is a single-purpose prompt/context extension plugin, not an interface/implementation/consumer capability seam: there is no swappable backend, only filesystem discovery plus per-request context injection. It depends on interface packages (`dsh-agent` and `dsh-llm`) plus the low-level `dsh-paths` utility for the shared DSH home convention, and consumes the existing `agent/request` waterfall.
 
 The plugin is loaded by `@deepseek-ai/dsh-agent-core` so both product front doors (`dsh-stdio-agent` and `dsh-acp-agent`) get instruction-file behavior by default. The bundle and both app packages expose `projectInstructions` config, so apps may set `projectInstructions: false` or `baselineMaxBytes: 0` when they need a hermetic prompt. The default product behavior matches user expectations for coding agents.
 
@@ -28,7 +28,7 @@ The first cut intentionally does not load lowercase variants (`agents.md`, `clau
 
 User-global harness instructions live at `$DSH_HOME/AGENTS.md`, where `$DSH_HOME` defaults to `~/.dsh` when unset. This mirrors Codex's `~/.codex` and Claude Code's `~/.claude` convention without inventing a repo-local home. The user-global file loads before project files so project-specific instructions appear later and can override broad preferences in the model-readable order.
 
-`$DSH_HOME` is a filesystem location only; this RFC does not introduce a broader config service. If a future config package owns the harness data directory, it should preserve this default and move the path resolution there.
+`$DSH_HOME` is a filesystem location only; this RFC does not introduce a broader config service. The default `.dsh` directory name and tilde expansion live in the small `dsh-paths` utility package so future features can share the same convention without depending on this prompt plugin. If a future config package owns the harness data directory, it should preserve this default and consume or supersede that helper deliberately.
 
 ### Project baseline discovery