feat(sdk): pluginRoot officiel exposé dans activate(ctx) — #285 (src/runtime: champ pluginRoot = racine du package installé; docs activation-context/commands-and-feedback/services/manifest réécrits du constat d'absence vers le contrat d'usage officiel — runCommand reste project-scoped, pluginRoot utilisable dans command/args, substitution manifest ${pluginRoot}/${appDataDir} inchangée pour mcpServers; exemple hello-plugin: script packagé scripts/hello-task.mjs consommé via ctx.pluginRoot, packaging étendu; QA verte: npm run check — build, typecheck:examples, package:hello-plugin, artefact zip vérifié)

docs/manifest.md

@@ -255,9 +255,10 @@ declared MCP server. In `command`, `args`, `env` and `cwd`, the host expands:
 - `${pluginRoot}` to the installed plugin package root.
 - `${appDataDir}` to the host-owned application data directory.
 
-This substitution is limited to manifest-declared MCP server startup. It is not
-available from `activate(ctx)`, `ctx.services.workspace` or
-`ctx.services.tasks.runCommand()`.
+This string substitution is limited to manifest-declared MCP server startup.
+Runtime handlers receive the same installed package location separately as
+`ctx.pluginRoot`; `ctx.services.tasks.runCommand()` does not perform placeholder
+substitution, and workspace APIs remain project-confined.
 
 ## Validation