feat(ipip-0499): document symlink handling in profiles

- add Symlinks parameter to UnixFS parameters list
- add Symlinks row to unixfs-2025 (TODO) and legacy profiles tables
- kubo: preserved, helia/storacha: followed, dasl: not specified
- add terminology for preserved/followed with UnixFS spec reference
- clarify kubo --dereference-args behavior

Author: lidel

src/ipips/ipip-0499.md

@@ -57,8 +57,9 @@ Here is the complete set of UnixFS parameters that affect the resulting string e
 1. Whether hidden entities (including dot files) are included in the DAG. Some implementations may apply filtering.
 1. Directory wrapping for single files: in order to retain the name of a single file, some implementations have the option to wrap the file in a `Directory` with link to the file.
 1. Presence and accurate setting of `Tsize`.
+1. Symlink handling: preserved as UnixFS Type=4 nodes, or followed (dereferenced to target).
 
-The handling of symlinks and symlink follows is defined by the [UnixFS](https://specs.ipfs.tech/unixfs/) spec.
+The [UnixFS spec](https://specs.ipfs.tech/unixfs/) defines Type=4 for symlinks with target path stored in the Data field.
 
 ## CID profiles
 
@@ -79,6 +80,7 @@ The initial profile in the series, **`unixfs-2025`**, captures the baseline defa
 | Leaves                        | raw                                                     |
 | Empty directories             | TODO (kubo needs opt-out flag)                          |
 | Hidden entities               | TODO                                                    |
+| Symlinks                      | TODO (preserved?)                                       |
 
 ## Legacy profiles
 
@@ -98,12 +100,15 @@ We also define a series of **legacy profiles**, used by various implementations
 | Leaves                        | dag-pb                         | raw             | raw                | raw                | raw                     | not specified |
 | Empty directories             | included                       | included        | excluded           | included           | included                | not specified |
 | Hidden entities               | opt-in                         | opt-in          | opt-in             | opt-in             | opt-in                  | not specified |
+| Symlinks                      | preserved                      | followed        | followed           | preserved          | preserved               | not specified |
 
 **Terminology:**
 - `included`: Always included in the DAG (no option to exclude)
 - `excluded`: Always excluded from the DAG (no option to include)
 - `opt-in`: Excluded by default; implementations provide a flag to include (e.g., `--hidden` in Kubo/Storacha, `hidden: true` in Helia)
 - `opt-out`: Included by default; implementations provide a flag to exclude
+- `preserved`: Symlinks stored as UnixFS Type=4 nodes with target path (per [UnixFS spec](https://specs.ipfs.tech/unixfs/)). Note: Kubo (v0.39) `--dereference-args` only follows symlinks passed as CLI arguments; symlinks found during recursive traversal are always preserved.
+- `followed`: Symlinks dereferenced and treated as target files/directories
 
 See related discussion at https://discuss.ipfs.tech/t/should-we-profile-cids/18507/