docs(rfd): Add RFD 060 for --explain config resolution flag (#466)

Add RFD 060, proposing a global `--explain` flag that traces JP's
layered config resolution chain, showing users exactly where each field
value originates.

The motivation: when a config value isn't what the user expects, there's
currently no way to find out which layer set it — file configs, env
vars, conversation deltas, CLI flags, and alias resolution all silently
compete. `--explain` makes that chain visible.

Two modes are proposed: broad mode (bare `--explain`) groups all
non-default fields by the layer that set them, and focused mode
(`--explain=<field>`) traces a single field through every layer
including "not set" and "not found" entries. Both modes support JSON
output via `--format=json`.

The implementation approach uses snapshot-and-diff provenance:
`PartialAppConfig` is cloned after each layer is applied, and `delta()`
is used to determine what each layer contributed. A `CliRecorder`
captures the CLI flag-to-field mappings including alias resolution
details. The flag suppresses command execution, following the precedent
of e.g. `terraform plan`.

---------

Signed-off-by: Jean Mertz <git@jeanmertz.com>

Author: JeanMertz

docs/.vitepress/rfd-summaries.json

@@ -234,5 +234,9 @@
   "059-shell-completions-and-man-pages.md": {
     "hash": "791b583757910d0f1687a180f4ec49fd2d7876ffd695ceffc546bcf4ae5b9c7c",
     "summary": "Add `jp completions` and `jp manpage` subcommands using clap_complete and clap_mangen for shell integration."
+  },
+  "060-config-explain.md": {
+    "hash": "cfa8458677aef01bb18793dab19605f67968b23ad00905a9d02dbd1bc7647bc0",
+    "summary": "Global `--explain` flag traces config resolution through 9 layers, showing where each field value originates."
   }
 }

docs/package.json

@@ -3,7 +3,7 @@
   "packageManager": "yarn@4.9.1",
   "devDependencies": {
     "typescript": "^5",
-    "vitepress": "2.0.0-alpha.16",
+    "vitepress": "2.0.0-alpha.17",
     "vue": "^3.5.16"
   }
 }

docs/rfd/059-shell-completions-and-man-pages.md

@@ -106,9 +106,9 @@ for your shell:
 
 `clap_complete` v4.4+ provides `CompleteEnv`, a dynamic completion system where
 the shell calls back into the binary itself when the user presses Tab. Instead
-of generating a large static script with all options baked in, `jp completions
-<shell>` generates a small shell script that registers `jp` as its own
-completer.
+of generating a large static script with all options baked in, the command `jp
+completions <shell>` generates a small shell script that registers `jp` as its
+own completer.
 
 When the shell requests completions, it invokes `jp` with special environment
 variables. JP inspects the partial command line and returns candidates. This
@@ -348,8 +348,3 @@ changing the shell integration mechanism.
   `--cfg` completions
 - `SchemaType::Enum` in `schematic` — enum variant extraction for value
   completions
-- [RFD D11]: Config explain — provenance infrastructure
-- [RFD D12]: Interactive config — `--cfg` browser
-
-[RFD D11]: D11-config-explain.md
-[RFD D12]: D12-interactive-config.md