chore(govdao): improve error handling in Render (#4910)

Fix: #4629 

Add more checks, fix interface call on nil, and enhance error messages
in GovDAO to create a more user-friendly experience.

I didn't add second check on `GetStatus` return value, as it should
never be triggered.
I'm not sure the `getPropStatus` UNKNOWN status can be executed, but
it's always great to have.

## Tests
#### Prerequisites 
```
// Install gno
gnodev . // In any directory
```

### DAO not initialized
- http://127.0.0.1:8888/r/gov/dao/v3/impl:1000 
<img width="1190" height="618" alt="image"
src="https://github.com/user-attachments/assets/aef433fa-f3eb-4948-9d34-dd20aaebc3c2"
/>


### Invalid proposal
For the next tests, you should load
http://127.0.0.1:8888/r/gov/dao/v3/loader before executing the test to
initialize the DAO.
- "No proposals yet." - http://127.0.0.1:8888/r/gov/dao/v3/impl
<img width="1324" height="956" alt="image"
src="https://github.com/user-attachments/assets/d8f6135a-a190-4518-8bf8-b1e092fa5dbf"
/>
- "Error: Invalid proposal ID format." -
http://127.0.0.1:8888/r/gov/dao/v3/impl:100a
<img width="1390" height="524" alt="image"
src="https://github.com/user-attachments/assets/3a37eeed-def0-446e-aad5-3b389eecb23c"
/>
- "Proposal not found" - http://127.0.0.1:8888/r/gov/dao/v3/impl:1000
<img width="1222" height="536" alt="image"
src="https://github.com/user-attachments/assets/b4031c5c-8713-41ec-ac55-c90034ac0893"
/>

---------

Co-authored-by: Manfred Touron <[email protected]>

Author: Davphla

examples/gno.land/r/gov/dao/proxy.gno

@@ -3,7 +3,10 @@ package dao
 import (
 	"chain"
 	"chain/runtime"
+	"errors"
 	"strconv"
+
+	"gno.land/p/nt/ufmt"
 )
 
 // dao is the actual govDAO implementation, having all the needed business logic
@@ -43,6 +46,9 @@ func MustCreateProposal(cur realm, r ProposalRequest) ProposalID {
 // If the proposal was denied, it will return false. If the proposal is correctly
 // executed, it will return true. If something happens this function will panic.
 func ExecuteProposal(cur realm, pid ProposalID) bool {
+	if dao == nil {
+		return false
+	}
 	execute, err := dao.PreExecuteProposal(pid)
 	if err != nil {
 		panic(err.Error())
@@ -64,6 +70,9 @@ func ExecuteProposal(cur realm, pid ProposalID) bool {
 // CreateProposal will try to create a new proposal, that will be validated by the actual
 // govDAO implementation. If the proposal cannot be created, an error will be returned.
 func CreateProposal(cur realm, r ProposalRequest) (ProposalID, error) {
+	if dao == nil {
+		return -1, errors.New("DAO not initialized")
+	}
 	author, err := dao.PreCreateProposal(r)
 	if err != nil {
 		return -1, err
@@ -97,6 +106,9 @@ func MustVoteOnProposal(cur realm, r VoteRequest) {
 // If the voter cannot vote the specified proposal, this method will return an error
 // with the explanation of why.
 func VoteOnProposal(cur realm, r VoteRequest) error {
+	if dao == nil {
+		return errors.New("DAO not initialized")
+	}
 	return dao.VoteOnProposal(r)
 }
 
@@ -119,11 +131,17 @@ func MustGetProposal(cur realm, pid ProposalID) *Proposal {
 
 // GetProposal gets created proposal by its ID
 func GetProposal(cur realm, pid ProposalID) (*Proposal, error) {
+	if dao == nil {
+		return nil, errors.New("DAO not initialized")
+	}
 	if err := dao.PreGetProposal(pid); err != nil {
 		return nil, err
 	}
 
 	prop := proposals.GetProposal(pid)
+	if prop == nil {
+		return nil, errors.New(ufmt.Sprintf("Proposal %v does not exist.", int64(pid)))
+	}
 
 	if err := dao.PostGetProposal(pid, prop); err != nil {
 		return nil, err

examples/gno.land/r/gov/dao/proxy_test.gno

@@ -79,9 +79,9 @@ func TestProxy_Functions(cur realm, t *testing.T) {
 		pid = MustCreateProposal(cross, NewProposalRequest("Proposal Title", "Description", e))
 	})
 
-	p := MustGetProposal(cross, 1000)
-	if p != nil {
-		panic("proposal must be nil")
+	p, err := GetProposal(cross, 1000)
+	if p != nil || err == nil {
+		panic("proposal should not exist and should return an error")
 	}
 	p = MustGetProposal(cross, pid)
 	urequire.Equal(t, "Proposal Title", p.Title())

examples/gno.land/r/gov/dao/v3/impl/render.gno

@@ -61,10 +61,15 @@ func (ren *render) renderActiveProposals(url string, d *GovDAO) string {
 	out += "[> Go to Memberstore <](/r/gov/dao/v3/memberstore)\n"
 	out += "## Proposals\n"
 	page := ren.pssPager.MustGetPageByPath(url)
+	if len(page.Items) == 0 {
+		out += "\nNo proposals yet.\n\n"
+		return out
+	}
+
 	for _, item := range page.Items {
 		seqpid, err := seqid.FromString(item.Key)
 		if err != nil {
-			panic(err.Error())
+			continue
 		}
 		out += ren.renderProposalListItem(ufmt.Sprintf("%v", int64(seqpid)), d)
 		out += "---\n\n"
@@ -78,10 +83,15 @@ func (ren *render) renderActiveProposals(url string, d *GovDAO) string {
 func (ren *render) renderProposalPage(sPid string, d *GovDAO) string {
 	pid, err := strconv.ParseInt(sPid, 10, 64)
 	if err != nil {
-		panic(err.Error())
+		return ufmt.Sprintf("# Error: Invalid proposal ID format.\n\n\n%s\n\n", err.Error())
 	}
+
+	p, err := dao.GetProposal(cross, dao.ProposalID(pid))
+	if err != nil {
+		return ufmt.Sprintf("# Proposal not found\n\n%s", err.Error())
+	}
+
 	ps := d.pss.GetStatus(dao.ProposalID(pid))
-	p := dao.MustGetProposal(cross, dao.ProposalID(pid))
 	out := ufmt.Sprintf("## Prop #%v - %v\n", pid, p.Title())
 	out += "Author: " + tryResolveAddr(p.Author()) + "\n\n"
 
@@ -102,10 +112,15 @@ func (ren *render) renderProposalPage(sPid string, d *GovDAO) string {
 func (ren *render) renderProposalListItem(sPid string, d *GovDAO) string {
 	pid, err := strconv.ParseInt(sPid, 10, 64)
 	if err != nil {
-		panic(err.Error())
+		return ufmt.Sprintf("# Error: Invalid proposal ID format.\n\n\n%s\n\n", err.Error())
 	}
+
+	p, err := dao.GetProposal(cross, dao.ProposalID(pid))
+	if err != nil {
+		return ufmt.Sprintf("# Proposal not found\n\n%s\n\n", err.Error())
+	}
+
 	ps := d.pss.GetStatus(dao.ProposalID(pid))
-	p := dao.MustGetProposal(cross, dao.ProposalID(pid))
 	out := ufmt.Sprintf("### [Prop #%v - %v](%v:%v)\n", pid, p.Title(), ren.relativeRealmPath, pid)
 	out += ufmt.Sprintf("Author: %s\n\n", tryResolveAddr(p.Author()))
 
@@ -122,9 +137,13 @@ func (ren *render) renderProposalListItem(sPid string, d *GovDAO) string {
 func (ren *render) renderVotesForProposal(sPid string, d *GovDAO) string {
 	pid, err := strconv.ParseInt(sPid, 10, 64)
 	if err != nil {
-		panic(err.Error())
+		return ufmt.Sprintf("# Error: Invalid proposal ID format.\n\n\n%s\n\n", err.Error())
 	}
+
 	ps := d.pss.GetStatus(dao.ProposalID(pid))
+	if ps == nil {
+		return ufmt.Sprintf("# Proposal not found\n\nProposal %v does not exist.", pid)
+	}
 
 	out := ""
 	out += ufmt.Sprintf("# Proposal #%v - Vote List\n\n", pid)
@@ -138,6 +157,9 @@ func isPropActive(ps *proposalStatus) bool {
 }
 
 func getPropStatus(ps *proposalStatus) string {
+	if ps == nil {
+		return "UNKNOWN"
+	}
 	if ps.Accepted {
 		return "ACCEPTED"
 	} else if ps.Denied {