attachments: link/unlink from the TUI, multi-voucher linksv0.1.29

The voucher detail can attach a file to an existing voucher (^F) and
the underlag picker (f) can remove a link (d, confirmed). The Underlag
inbox links a highlighted item to a voucher picked from a list (k).

attachment.link and attachment.unlink are new write commands (dry-run,
audited); unlinked files return to the inbox. The same content may now
link to several vouchers — only the same voucher/attachment pair is a
CONFLICT, matching the table's primary key.

3 files changed, 14 insertions, 6 deletions

diff --git a/docs/PROTOCOL.md b/docs/PROTOCOL.md
index e3e629b..75f384f 100644
--- a/docs/PROTOCOL.md
+++ b/docs/PROTOCOL.md
@@ -351,11 +351,17 @@ required.
 |---|---|---|
 | `attachment.put` | `filename`, `mime`, `content_base64`, `voucher_id?` | ≤ max_attachment_bytes |
 | `attachment.get` | `id` | returns base64 + sha256 |
+| `attachment.link` | `id`, `voucher_id` | write; audited |
+| `attachment.unlink` | `id`, `voucher_id` | write; audited |
 | `attachment.list` | `voucher_id?`, `unlinked?`, `limit`, `cursor` | inbox = `unlinked:true` |
 
 Attachments are immutable and content-addressed by SHA-256. They are linked to
 vouchers at posting time (`attachment_ids`) or afterwards via
-`attachment.put` with `voucher_id`; links are separate insert-only rows.
+`attachment.put` with `voucher_id` or `attachment.link`; links are audited
+rows, and `attachment.unlink` removes one (an unlinked attachment returns
+to the inbox). One attachment may be linked to several vouchers (the link
+key is the voucher/attachment pair); linking the same pair twice is a
+`CONFLICT`.
 
 ### 7.6 Reports
 
diff --git a/docs/STATE.md b/docs/STATE.md
index 0e5d36e..517e62a 100644
--- a/docs/STATE.md
+++ b/docs/STATE.md
@@ -82,10 +82,10 @@ server/protocol/ledger only.
 
 ## Pending decisions
 
-- Link attachments after posting (API already supports
-  `attachment.put {voucher_id}`): proposed TUI actions — `Ctrl+F` in the
-  voucher detail to upload+link, and selecting an inbox item and pressing a
-  key to link it to a voucher picked from a list. Waiting for a go-ahead.
+- Attachments are complete: download (voucher detail `f`, Underlag `Enter`,
+  SHA-256 verified, text inline), attach to an existing voucher (`^F`),
+  remove a link (`d` in the `f` picker) and link an inbox item to a voucher
+  (`k`).
 - Next backend milestone: **bokslut automation** vs **K2/SRU** (eSKD is
   done: `report.vat_eskd` + `s = spara eSKD` in the momsrapport).
 - Moms `report_rules` seed is a corrected starter mapping (schema v3), but
diff --git a/docs/TUI-GUIDELINES.md b/docs/TUI-GUIDELINES.md
index acb3748..a54fef8 100644
--- a/docs/TUI-GUIDELINES.md
+++ b/docs/TUI-GUIDELINES.md
@@ -29,7 +29,9 @@ there.
 | `a` | Add/upload (Underlag) |
 | `c` | Correct (voucher detail) |
 | `d` | Delete/arkivera the selected row (only where the action exists; asks for confirmation) |
-| `Ctrl+F` | Attach a file (voucher form) / pick a file (Underlag) via the file browser |
+| `f` | Voucher detail: list the voucher's underlag — Enter fetches, `d` removes the link (asks first). Underlag: Enter fetches |
+| `Ctrl+F` | Attach a file via the file browser (voucher form and voucher detail) |
+| `k` | Underlag: link the highlighted attachment to a voucher picked from a list |
 | `Ctrl+X` | Clear the current row — only inside row editors (never "new") |
 | `Ctrl+Enter` | Save/post the current form. Enabled via xterm `modifyOtherKeys`; terminals that cannot send it keep `F9` working |